A brief aside before we continue. Recruitment is only one side of the membership equation; the other side is activist retention. Many things can keep activists going, like success, camaraderie, and a sense of momentum. But there are just as many ways to lose members. One way is to fail to take care of people. Activists need emotional support and morale boosting, especially when things are not going well. Unless your group has a morale officer, that responsibility falls to everyone. Another way to lose people is to fail to appreciate them. Few activists get paid for what they do, and most campaigns are protracted. Good work and long-term commitment should be recognized and celebrated.
Some people are especially good at doing these things of their own initiative, and these people should be nurtured and encouraged for the good of the group. Of course, there are also people who are very bad at these things, who constantly criticize new members for doing things differently, who engage in self-righteous cliquishness, and who generally make people miserable by being poster children for horizontal hostility. More prevalent in groups without experienced and well-behaved role models, these cranky activists are poison for activist retention.
People like this should be politely told to cut it out. If they can’t or won’t stop, either kick them out of the group or start a different one. Any group where such people hold sway will stagnate or self-destruct in the sort of way that causes lasting animosity and bitterness.
You are much less likely to have these kinds of problems if you screen people in the first place.