The line should be what is illegal, which, at least in the US, is fairly permissive. The legal process already did all the hard work of reaching consensus/comp

The line should be what is illegal, which, at least in the US, is fairly permissive. The legal process already did all the hard work of reaching consensus/compromise on where that line is, so just use that. At least with the legal system, there's some degree of visibility and influence possible by everyone. It's not some ethics department silently banning users they don't agree with.