At least most led groups have some way of keeping a reign on what their members do, keep them from doing stuff that casts the group in a bad light.
I can easily name several groups that have leaders who either ignored what their members were doing or basically condoned bad things (but I'd be violating several forum rules and probably get myself banned in the process). Leaders do not always have a tight leash on group members - in some cases the opposite is true. The simple presence of a leader does not necessitate that said leader has control over group members, or will even try to intervene or do "the right thing."
Let's make one thing clear, I don't hate a lot of what anonymous does, like Next's example where they caught those guys putting up animal torture vides on youtube. That kind of thing is good. However, I don't like the group itself because they lack any kind of restraint, and that's what comes back to bite them (and a lot of other people who have nothing to do with them for that matter) all the time.
The funny thing is, Anonymous is made up of people - people decide to do the things, both good and bad, that are attributed to Anonymous. They have the same level of restraint that anyone else does - which is to say only the restraints that they place upon themselves.
At least they do something and stand for their convictions, which is more than I can say about a good many people.
This. Very much this.