I see what you're saying, but I think what you're missing is that this isn't "the right kind of person", this is literally checking to see if you're a child molester. There's no slippery slope here. They do a background check and say "is this person a literal kiddy fiddler?"
Could WOTC eventually turn the background check into some sort of purity test? Yeah, sure, eventually maybe (although that would kinda be exceptional because first and foremost WOTC and Hasbro exist to turn a profit and excluding players on dubious moral grounds is a great way to kill your product). But should we just shit on the entire idea on the basis that there might be a slippery slope, maybe, at some point in the future possibly? I don't think so.
As far as the public sex registry goes, as a large company I'd be more comfortable with paying a firm to do a real background check versus having some minimum wage employee google sex registries. I'm almost positive this would be required as some sort of legal CYA thing.