Many people don't have a choice for school. They can't afford private school or charter. They can't homeschool. All they can do is send their kids to the public schools.

Kids are impressionable and easily confused. The idea you can just pick a gender and can change it whenever you feel like is incredibly damaging to society.

It spreads. All ideas that are within a large enough group, can spread. You can make societies do all kinds of things. Just because more and more believe in those things, don't make them correct, moral, just, or beneficial to humanity. As an extreme example, people used to collectively sacrifice other people just to make it rain. The majority all thought what they were doing was 'good, virtuous, and great'.

Being concerned with the implications of confusing 4 year olds (basically toddlers) about their gender is not 'hate' - it's the opposite.