Homosexuality is not a mental illness. But Homophobia is.

All that they are trying to do is that to raise awareness that they exist, and they are asking everyone to not discriminate them based on their sexual orientation, gender identity or gender expression.
If you are okay with respecting people regardless of those things, then you are a good person and the world needs more people like you. Also, you are following a growing trend because more and more people are starting to accept LGBT+ people. I can assure you there will be less of all these 'phobes' in a couple of decades because they are a dying breed.