The lack of a positive doesn't make something morally wrong.

The lack of a positive along with the existence of negatives does, however.

The "trust" thing is a rather weak argument. I think society would continue to function if disabled people were "euthanized."

It would also continue to function if we killed and ate half of the babies that were born.

I'd rather have a better society than a functional one.

Besides, what if it's a genetic disability that I'll never get?

Saying "lets kill everyone with a disability because they aren't productive" does not only specify genetic disabilities. Saying "lets try to cut out genetic disabilities" cannot be done without also cutting down diversity and hurting humanity more than you help it.

How do you think eating animals makes vegans feel?

Unless the vegan knows the animals in question personally, I honestly don't care. The question of "I think this is immoral" is different than the question of "you killed my pet". It is not traumatizing for vegans to know that other people eat meat. It is traumatizing to have your kid killed for the better good.