I sent a movie script to an agent who offered a critiquing service. The people who attend the meetings are mostly people who genuinely want to write, improve their writing, and maintain contact with other writers. Formal writer's groups, like those associated with arts councils, are usually attended by people who are reasonably sensitive to others needs, and who typically don't assault each other s esteem. Writer's groups are never perfect, so be prepared for their peculiarities. The membership of groups is fairly dynamic from year to year.
Many writers stay indefinitely, but others move on, burn out, or lose interest.
New faces show up regularly - fewer than half come back. Groups typically split every year or so as special interest groups congeal, and form their own group, as in children's writing, women's issues, science fiction writing, screenwriting, playwrighting, romance writing, and poetry. If these differing groups aren't flexible, tension develops and people leave. Sex scenes and foul words, which may be legitimate to the story, may not be well received in a group. Test the waters before jumping in.