Why we should make as little conduct as possible illegal.
Laws are outcomes in the political process that affect how people can (legally) live their lives. To minimize to the greatest extent possible the extent to which some people (even a majority) are determining how all people in a community might choose to live their own separate lives, laws governing the actions of people should be restricted to prohibiting conduct that necessarily causes obvious, knowable harm to other people (though such harm might be, as well as material, of a psychological nature, such as behavior that is threatening to another person). That maximizes liberty.
To have liberty to live one’s life as one pleases (short of acting illegally), one must be willing to allow others to live their lives as they please (subject to the same limit). That is why the forms of conduct that are made illegal should be restricted as much as possible.
Just because I think certain conduct is wrong does not mean it has to be illegal. Others might not think it is wrong. Just because it is legal does not mean I am required to engage in it. To make such conduct illegal because some people think all people must be delivered from that temptation is to go too far in imposing some people’s personal morality on others. Harms to other people that did actually occur from legal conduct might in themselves be illegal, and if not could still be addressed via civil litigation.
To live in a society in which certain conduct one believes to be wrong is legal is not the same thing as endorsing it or even condoning it. It is recognizing the limits necessary in law-making for coexisting people to enjoy the maximum possible liberty.