If most liberals seems to believe in the "blank slate" theory where our traits are shaped by nurture instead of nature, why do they at the same time consider homosexuality to be complete innate ie, nature?

Gabriel Seah's answer to If most liberals seems to believe in the "blank slate" theory where our traits are shaped by nurture instead of nature, why do they at the same time consider homosexuality to be complete innate ie, nature? - Quora

It conforms to their ideology.

The underlying liberal premise here is that discrimination (or differential treatment) based on immutable traits is discriminatory and wrong (Page on iit.edu).

Liberals do not want to discriminate against people based on immutable traits, but at the same time they want to retain the ability to discriminate based on certain factors.

For example, it is justifiable to not hire the lazy and the stupid, or to pay them a lower salary (some commentators go even further and point out that we don't choose to be lazy and/or stupid [Do Smart, Hard-Working People Deserve to Make More Money?] and so there is some justification for not paying them less, but I won't go into that, not least since it involves talking about free will).

So, if homosexuality is entirely due to nature and is immutable, then this is reason to accept it and not to discriminate against homosexuals (since homosexuals are supposedly born that way).

At the same time, if other traits are shaped entirely by nurture, then we can discriminate based on them. For example we can not hire the lazy and the stupid, or pay them a lower salary, with the underlying assumption that they could've done otherwise (since these traits are entirely or mostly shaped by nurture and the individual has some control over them); the concept of moral desert (of getting what you morally deserve - Desert (Stanford Encyclopedia of Philosophy)) is implied here.

Liberals also believe in the potential for social change through social engineering. So welfare, affirmative action or ending stereotyping can counteract the influence of other social forces (i.e. nurture), leaving us in a situation where outcomes are equal (since they believe that if we correct for social forces such as discrimination, we will all turn out the same way since our traits are only shaped by nurture).

As a concrete example, feminists generally assert that men and women are the same, so the gender wage gap must be due to discrimination, stereotyping, social forces keeping women at home etc. And putting an end to discrimination, stereotyping and social forces keeping women at home will lead to the gender wage gap disappearing.

One notes that there are 2 linked fallacies involved here: the naturalistic fallacy (what is natural is good/right) and the moralistic fallacy (if it's not good/right it can't be true). This is why they are so quick to reject explanations of group differences in traits that point to nature (e.g. that there is a biological basis for the math gender gap)