Imagine a movie is great. It has a great pacing and characters go through proper development. Now imagine it gets a just as good sequel. Everyone loves it. Kids, adults and everyone in between. 

This time, imagine that companies start to focus on the comedic side characters and use them for advertisements. They end up everywhere. Now there is no merchandise of the main characters that were the ones to go through development and that we love. Eventually, due to the companies vastly misunderstanding what people enjoyed about the films, the side characters who were only there for comedic purposes have completely overtaken the series to the point where they get their own movie which completely retcons what character they did have.

That is where the hate for the minions comes from. They were just for comedic purposes in the original movies and what we DID know about them was that gru created them from corn. Then they were overadvertised and completely drowned out the characters people actually did like such as gru, the sisters and vector. it’s now like they don’t even exist. The hatred for the minions comes from the erasure of what made the original movies good.