In my opinion, it's fine if a business doesn't want funds that come straight from an online casino for example, as long as they don't call a coin 'forever tainted' if it once came from such a casino.
But then the casino could do the same and just transfer their funds to a new wallet and then use them again. Just trying to taint a coin for whatever reason creates a whole lot of unnecessary problems.
I think what n0nce meant is: It's okay for a business to not want to be included into illicit activity and fight it, but that should happen as long as they don't invade in people's privacy and enforce non-effective tactics that do more harm than good, if they do any good at all.
Unfortunately for businesses that accept bitcoin, there's no way to
try to prevent criminal activity, without harming their customers, because there's no way to do in cash either way. Ultimately, there's no way for these businesses to prevent criminal activity.