If you're referring to the engineers exploit, not every SDC member used the exploit, and it should be known that it was the 13th legion that publicized it after it had been repeatedly reported by SDC members privately to frontier. Many players used the exploit, and the offenders had all relevant modules removed, as well as many more legitimate modules. Some people seem to forget that part.
Anyway, blocking is not foolproof. In fact, instancing prioritizes friends list chains over the block list, and sometimes you instance with blocked players seemingly randomly as well. But most importantly, even when the block function DOES work, you can't use it as a PvPer. Because it will lock you out of the popular instance where everyone is doing things at the CG or wherever you happen to be. A CG gets dropped, people flock over, instances populate with players, and then you come on in. All your pvp friends are in the instance, but so is your blocked clogger. When blocking DOES work, you're getting locked out of the instance with all your friends. Otherwise, you do get in, and the clogger is there anyway. Blocking is wholly a bad thing if you want to do PvP. That's why almost every pvper has a clean block list, as it provides almost no benefits but brings a whole slew of problems with your instancing abilities.
