It is all about conditioning, IMO. They can be dealt with, and they can be abused. Just like anything else in this, or any other fighting game. So no, in proper context I do not see it as a "scrub tactic". I play offline and even in casuals I love hearing my opponents bitch about and get salty over cross-ups. You know why? Because at that point, I am in their head...Play to win.
I can see the gripes people have with the fact that a blocked jip jails and they are a bit OP when relatively compared to other games. BUT, this is not other games and any fighting game has it's subjectively undesirable elements when compared to other titles. (That was not an arbitrary, "RAWR THIS IS MK, BITCH" type of statement...no fighting game is "other games")
The fact remains, however, they are in the game. So ADAPT. Online is one thing when you get your anti X-up stuffed, but offilne, if you have conditioned your opponent and they are are not taking care of business with regards to cross ups....abuse that shit. Play to win, man. Learn the meta game and play to win.
This mentality has helped me greatly with respect to getting abused by cross-ups. I know when its online, and I know when I fucked up or got caught slipping. Simple as that.