I like the no trolling rule. Lolcows don't need to be prodded to provide entertainment, at least not by us.
I think it's also very important to the site's survival. We are here to make fun of what people voluntarily put online. If a cow doesn't like what's being said about them here, they can ignore it or stop putting their shit out in public. That they can't fathom the latter is what makes them cows. We aren't harassing anyone, no matter what they say.
That being said, I'm sure there's a bunch of people who troll. It's not endorsed by the site, but if you don't brag about it and expect to get asspats for it, how would we know. But I think it's not as many users as you presume, because a lot of people who blame all their trolling on the Farms have made many enemies through their behaviour in many different places.
A lot of cows have people that have much better motivation to actively fuck with them than we do. There's a few grey areas, but the site being against trolling is what makes it far more interesting. Observing and documenting is better than the site descending into a group of people bragging about being blocked by a cow for calling them a retard.