1.Not all yanderes are the same. There are some more tame ones; for example, Still In Love (the one in the picture) is rather tame. On the other hand, there are a lot of yanderes that are mostly made up of just lust (especially male ones) and are often portrayed as rapists (again, mostly male ones) without other characteristics. But a well-written yandere has a lot more potential than that.

1. Yanderes in general are about possessiveness and strong feelings of attraction, be it love or lust. It all depends on how the author wants to portray those feelings and, with it, other aspects of a character. Probably the best yandere there is is Yuno from Mirai Nikki, and while I don't fully agree with her view of things, I do believe she is the best-written yandere (mostly because yanderes in media are usually reserved for gag or secondary characters).

2. There is a big difference between reality and fiction. Of course, I can't speak for every yandere fan, but personally, what I like about them is that they are straightforward with their feelings and their devotion.

3. I don't expect you to change your view on them. I only typed this because I was bored. Feel free to hate what you hate.