I probably wouldn't blame the members who posted after the thread got bumped, because they might not have noticed what the date was in the OP. I've done that quite a few times by accident, and it's a mistake anyone can make--so IMO the blame falls squarely on the person who actually bumped the thread.
I don't agree with you. It's their fault that they haven't checked the date. Most of these users just came to that thread to leave generic reply in order to reach their post quota and they didn't had intentions to make contribution. Though it's not worst example that we can find. It's not half year old topic which was inactive for few years. I'm not sure that all these users who posted after necrobump deserved to get banned. I haven't checked their post history, but if they posted in such topics just few times, it would be to strict penalty to ban them from campaign.