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.
I don't agree with you because the way that you establish if a thread is active is by looking at the latest posts and if they are recently then you assume that the topic has remained active after all of these years and this is definitely true when the reply is substantial. I would not blame the members posting after the necrobump unless their replies are spam too. The only criticism that could be given is if the thread is a megathread but if its a thread which was posted a year ago and then six months ago it was necrobumped you would probably read through the whole of the thread but only check the dates of the last couple of replies.