If it's players that went to CC or had injuries, I have less of a problem with it. Give them their chance to play their four years at the D-I level. Grant-Foster is a very interesting case, not the least of which is because he was getting NBA Draft buzz a couple of years ago.
What I struggle with are 21-22yos coming over from Europe that have played professional ball for 3 years already (like Uros, though obviously he didn't come over here to play major minutes). The kids coming over at 18 or 19, even if they've been on pro rosters, I'm generally fine with (like Rrezon).
What I can't stomach are guys that have played G League ball coming back to college. In no world should that be allowed.