Basically, one of the things that makes farming keys and uber bosses (one of the big draws of the last major patch) possible is a well geared CM wizard. Ask Contra- I don't like to brag, but the only uber fight that gives us trouble on the regular is Leoric/Maghda, and that's because she will go invulnerable AND I CAN'T FREEZE HER. Rakanoth and Ghom are both too slow and easy to freeze both at once; as long as I can get a good lock on Kuule and Siegebreaker, I can keep them in check too- I have over 1k life on hit, 50%+ crit chance. I am an invulnerable, tornado shitting, diamond skinned avatar of death that is constantly supernova-ing 'asplosions while keeping our enemies permanently frozen, more or less.
It cost a shit ton of time, gold, and AH finagling to get here. And my dps isn't even that impressive- it hovers around 100k depending on my gem loadout, but paper dps for the SNS CM variant I run is a poor indicator of just how much damage I do, since anything that's frozen takes 20% more damage due to a passive, and anything that's frozen with frost nova takes 15% MORE damage due to the rune I've got selected.
Basically, there's no way you're going to tell gamers who spent that much time, effort, and in some cases money that they can't use that shit as effectively in pvp, and I think Contra is right- it would totally imbalance pvp to the point where it's "kill me before I can freeze you, bitch"