Not necessarily imo. There would be a real precedent set in allowing such as clause in a player's contract and I'm sure United wouldn't enter into such an agreement lightly. If the club has decided that they don't want to entertain contractual demands for game time then I find it a little presumptuous to call them stupid outright; it's a contentious issue that needs exploring more deeply before jumping to conclusions one way or another I believe. It doesn't matter who the player is; if the club decides on principle that these clauses are something they won't abide by then that's the end of it. It could yet prove to be an excellent decision.
The point is though that we wouldn't lose anything. If Thiago isn't good enough for us and doesn't play in 60% of the minutes (thinking about a similar clause like he had on Barca) leaving him to go for a similar fee for what we signed him, isn't a bad thing. I mean, the chances to get more than around 20m for a bench midfielder of Man United isn't that high.