I kind of feel like the progressives' roots in eugenics is still a major driving ideology, although expressed a bit differently now. The liberal ideology seems to be that once a person exists, no matter how mentally ill, deluded, or criminal they are, we need to respect them and make a place for them in society. But we'd rather not have them exist in the first place. So we make a place for everyone, but also highly encourage behaviors that would result in producing fewer people. Abortion, acceptance and celebration of homosexuality, narcissism, incelism, obesity, general physical and mental weakness.
The conservatives' ideology isn't as clear to me, although it seems to have something to do with personal responsibility. Since pro-life/anti-abortion is a major part of the conservative platform I would say the attitude is that everyone should at least get a fighting chance in life, although some may be highly disadvantaged. Then, in adulthood, those that don't make the cut can't be tolerated at all. The conservatives aren't really clear at this point about what their solution is. What I see in practice is that the conservative solution is to just get rid of the undesireables as adults, by putting them in jails or making conditions so bad for them that they have no choice but to flee to liberal cities where they'll be accepted. In a way I kind of see this as violating the personal responsibility part of conservatism. If your family or culture has produced people you don't like, it's your collective responsibility to deal with them, not just ship them off somewhere else for others to deal with.