Answer:
Many people grow up with that being their normal. Put it this way, if you were born into a cult that worshipped grass, you're going to grow up thinking that grass is god. Regardless of what everyone else tells you, from the time you were born to now, you were taught: grass is god. It's the same way with discrimination. Whether we like it or not discrimination is still around and the thing that keeps it alive, is us passing it down to our children.
Another reason is some people don't understand it. Humans fear the unknown, even if they don't admit it, it's a natural instinct. It can be from the color of one's skin to another's sexual preference. Some people don't understand it and don't wish to understand, and while that's ok, it's not ok to take it out on others.
Finally, many people have conflict with themselves. There's a great deal of homophobes who are apart of the LGBTQ+ Community, and because they are so in denial about it, they go to extreme. I'm not saying that's all of them, but there are a few.
Another situation following the last, could be an abusive parent. They could call you many slurs and say awful things to and about you, or get physical. That's a sign that they have unhealed trauma, conflict, and even abuse. It's not an excuse but it's a reason.
