It's pretty obvious there's an anti-Muggle (and probably, though not shown, anti-Muggleborn) bias in Wizarding society considering how the Daily Prophet reported on them to even how the usually tolerant Weasleys spoke about them.

So you could fanwank that most people were ok with the anti-Muggleborn thing because they believed Muggles could steal magic and wanted to weed them out. Like the Muggleborns they knew were ok but it's those other ones you have to watch out for.