Well, fans ARE toxic a lot of the time regarding these properties. Harassing, abusing, and threatening other human beings for the ATROCITY of making a fictional story in a way they didn't like.
**The following is pure speculation**
And while this is pure speculation on my part, it's my personal feelings that the suicide of Zack's daughter, was probably, at least in part, fueled by shitbag fans who can't separate their obsession with fictional products from reality. And that they probably gave her so much shit because "your dad's a fucking hack who DESTROYED batman and superman!" that she got tired of it. And I don't think that's a very big leap personally. We know from previous actors, like the guy who voiced JarJar, that the amount of hate people think is totally justified to throw at a stranger, can drive them to contemplate suicide. And teenagers are already in a high risk for suicide due to social pressures, and that social network technology makes it a lot easier for bullies to be bullies. It wouldn't surprise me at all to learn that his daughter, already emotionally shaky due to just simply being a teenager, possibly got tired of all the normal ridicule she might've endured, AND fanboy hate, that she did what she did.
**The proceeding is pure speculation**
So yeah, saying fans can be toxic, and be a problem, is a perfectly valid criticism. Even discounting my above statement, you just have to look at how a lot of them behave to know that's true.