Which is exactly what they shouldn't be doing, and what they're going to do is irrelevant and entirely separate from the point. If they so choose to not actually read the rules, then they're going to mess up and one of the mods is going to notice and ask them not to do it again. Once again, this isn't a huge problem, and technically auto merge is redundant because it takes the same amount of clicks to edit, type the message, and save as it does to hit the new reply or quick reply button, type the message, and send it.
No, we do complain that new people do it, because it's against the rules. Which new people would know if they read them. But they don't, and here we stand, so we tell them not to double post. And then occasionally you get someone who doesn't like it and suggests we implement a new feature to eliminate something that is totally within their control to stop anyway.