A concise description of what rules I think society should follow. I'm a leftist and a pacifist, and I emphasize science and health in my view of the role of government.
I could be described as a leftist, a progressive, a liberal, a feminist, a socialist, or a democratic socialist. I say this not because my commitment is to e.g. leftism itself and my opinions on the issues follow, but because "leftist" seems like a fair description of my opinions. In general, this is how political labels should be understood.
One of the most basic and fundamental moral rules is not to kill other people. In practice, killing is widely accepted for defense (of oneself or others) and as a part of war or revolution; and when people advocate for war or revolution, they usually do so in terms of defense. This is fundamentally wrongheaded, because it's no more moral to kill a killer than anybody else. Furthermore, people, when afraid for their lives, are quick to kill on a weakly justified suspicion that the other person will kill first, so the universal belief that killers should be killed is probably the most common reason that people kill in the first place. The only way for humanity to escape this trap is for us to not kill, to be openly unthreatening and unarmed, accepting the possibility that we'll be killed. This philosophy is what I call pacifism, and applies equally to ordinary people, the police, and states.
Nonlethal force, unlike lethal force, is sometimes justifiable, such as tackling a mass shooter. But you're morally required to use the minimum possible force. It's no more correct to punch somebody for fear they'll punch you first than to kill them for fear they'll kill you first. Police should be held to an especially high standard with respect to not using excessive force, because their purpose is to enforce basic moral rules, pacifism not the least of those rules.
Abortion is fine. An individual human doesn't count as a person until they're born, the same way that they're no longer a person after they die.
Animals aren't of any inherent moral importance the way that people are. It's not wrong to kill animals or make them suffer, excepting circumstances such as killing other people's pets or livestock, or hunting species that people have voted to protect because they're endangered.
The purpose of government is to pool humanity's resources and use them to improve the welfare of all. More concretely, governments should support health, safety, education, and research, and prevent people from doing evil. Governments can use force, but every restriction on people's behavior needs to be justified in terms of the best available empirical evidence about the restriction's effects, given how the restriction will actually be enforced. Any governmental function or lack thereof, restrictive or not, is only legitimate if approved of by the majority of the governed.
One person, one vote. Everybody who's subject to a government should have an equal say in its functioning, regardless of gender, race, age, education, and criminal history. Notice that this includes children. In the US, the Senate and the Electoral College both violate the rule of one person, one vote.
Direct democracy is better than representative democracy, because representatives often fail to represent their constituents accurately; in particular, they're vulnerable to corruption.
All people are unconditionally entitled to health and safety, including adequate food, clothing, shelter, and medicine, and it's the government's job to provide these to people who don't have them. When there isn't enough for everybody, the government must help as many people as it can.
So long as the weight of evidence supports interventions such as hormone therapy and sex reassignment surgery as the best treatment for gender dysphoria, such treatments should be just as available as any other legitimate medical treatment.
People shouldn't be unconditionally free to say whatever they want whenever they want, because some speech (like bigotry, calls for violence, or dangerous pseudomedical advice) is harmful, at least in some contexts. But legal restrictions on speech need to be no less well justified than other legal restrictions.
"Intellectual property" is ridiculous. It makes sense to require that people attribute works that they copy, but not to prohibit copying or modifying preexisting information, whether it's text, video, software, or something else. Copyright, patents, and similar systems should be abolished. So long as they still exist, such systems should only be used for copyleft.
One's religious beliefs should grant no exceptions to the laws everybody else has to follow. But again, any restrictions on religious practice need to be justified. The justifications of laws themselves, being empirically based, must be secular.
Some human changes to the natural environment, such as global warming and pollution, are major threats to human health, so ameliorating them should be a high priority for government.
If trade has any place, it's as a means to an end. The rich aren't morally entitled to their wealth simply because they have it at the moment, nor must the poor be poor.
Criminal law is for prevention and rehabilitation, not vengeance. Making evil people suffer needlessly isn't good; it's only answering evil with evil. Besides, it's more important that courts avoid misidentifying the innocent as guilty than the guilty as innocent. Otherwise, criminal law is a solution worse than the problem.
The death penalty
The fundamental problem with the death penalty is that dead people can't be brought back to life after we realize that we killed the wrong man. For all the ways that the courts can be improved, they'll never be perfectly accurate in their decisions of guilt and innocence, so there will always be wrongful convictions. The harshest punishment a criminal court imposes should be life imprisonment or exile.
Recreational drugs, including currently legal ones like alcohol and tobacco, are a blight on humanity, and their harm must be reduced as much as possible, which in practice may mean legalizing them. Drug policy should be guided by empirical science with the goal of maximizing population health. The government should never endorse recreational drug use, as by providing alcohol at a state function.
Sex work, such as prostitution and professional pornography, is generally abusive, because the typical modern society harshly punishes those who don't work, and not every sex worker has a non-sexual option that's economically just as good. In other words, consent to sex requires the ability to freely decide not to have sex, and a sex worker doesn't have that freedom, so e.g. paying a prostitute for sex is rape. Society should ensure that nobody has to resort to sex work.
In general, people should be treated according to their behavior rather than their bodies or ancestry. And in the name of maximizing collective human welfare, we should encourage the peaceful cooperation and coexistence of all sorts of people.
We shouldn't hold people morally accountable for involuntary characteristics such as sex, race, age, and sexual preferences, because people are only morally responsible for something to the extent they can control it. (In other words, to be immoral is to make an immoral choice.) Thus, for example, criminal law can't treat men differently from women or black people differently from white people merely because men and black people commit more crimes per capita than women and white people do.
Affirmative action makes sense, but only when implemented in a way that's transparent and quantitatively justified. For example, if 20% of a college's applicants are black and 80% are white, the college could admit a class that's 20% black and 80% white. Gratz v. Bollinger seems to imply that a quota system such as this is currently illegal in the US.
Bigotry against oppressor classes
In the US, racism against white people is less dangerous in practice, and less common, than racism against black people, but it's still immoral, and for the same reason. The same goes for bigotry against other oppressor classes such as men and heterosexual people.