Leaving aside ethical and moral considerations, the whole policy of Salazar Slytherin's "we should not teach muggle-born magic-capable children" seems to be completely counter-productive to the whole "Let's not allow Muggles to know about existence of magical world" idea.
To wit, muggle-born wizards are obviously capable of performing magic (there were several examples in the book) even without wands/training, and many of them are powerful enough as far as their magical ability that it's likely to get noticed.
So, short of killing off every child that has latent magical abilities (or at least those with abilities beyond some threshold) or charming them so they are unable to do any magic, wouldn't refusal to teach them all how to PROPERLY use magic and what the rules are merely get a lot more chances for Muggles to see magic being performed which totally goes against the whole "Let's not allow Muggles realize that there are magic users around" that drives a lot of the Wizarding rules?
UPDATE Just to clarify - this question is about the idea of Salazar Slytherin himself and not the modern-day Death Eaters/Voldemort.