Harris failed to distance herself from positions that are deeply unpopular with the majority of Americans (e.g. sex changes for illegal immigrants). That's all there is to it.
If you want to step away from this particular issue, she failed to distance herself from the Biden administration's policies. There's a pretty famous clip of her failing to answer a question to that point, definitely on the youtubes.
You're excluding a key point - the policy often benefits one party at the cost of another. You mentioned immigration and that's a great example of this sort of pathological empathy that has infected the left.
There's a cheap and fleeting sense of virtue attained when you champion illegal immigration and decry deportations. You post photos of mothers and their children crying at the border because the human trafficking organisations are having a hard time getting them across nowadays. But it's important to remember the negative pressure illegal immigrants place on wages and why there's a gross cabal of large corporations, lobbies, and affiliated NGOs, who virtue signal immigration as a means to lower their labor costs. It's important to remember the entire pipeline of illegal immigrants is owned and operated by extremely violent cartels - humans are now their most valuable product. Your desperate craving for that high of in-group acceptance is propping this up.
It's not that you're empathetic - you just don't care about the negatively impacted party. Nothing new under the sun.
I made no assertion about the criminality of the immigrants, but rather the cartels bringing them here.
Regarding "trans rights", which is quite a large umbrella of ideas, negatively impacted parties include:
1. Parents who don't want schools influencing their children's ideas about sexual identity.
2. Women who don't want to compete against biological men in athletics (this is the most bewildering failure of the left's tolerance).
3. Women who feel uncomfortable sharing previously women-only spaces with biological men.
4. Trans people who made life-altering decisions as a minor and now regret it.
These negatively impacted parties are vocal now - they aren't hard to see. You don't care about them, is all.