If he hated kids to the point of ignoring the racism/bigotry against him from a group known to carry out ethnic cleansing, he wouldn't have the job in the first place.

 

You're assuming that he had other job options. I imagine, that as a squib he'd find it difficult to find work.

 

...

Let me be clearer.

Who the fuck would give a job to a man who hated kids more than he hated a group that wanted to kill him and everyone like him?

 

I think the only reason JKR put Filch in the story was to introduce the idea of a Squib.

 

Been a while since I read the books, but I don't recall anything about him supporting the Death Eaters, or about the Death Eaters killing Squibs.

He did support Umbridge during her time as Hogwarts High Inquisitor, but that's another matter. Plus Umbridge seemed to at least treat him reasonably well, since he was pretty much the only Hogwarts Employee who actually supported her.