Your idea completely destroys what a forum should be. Can you just imagine how could you practice free speech in a forum when all of your posts will be subject for approval? You simply can't! all your replies will be subject to the moderators reviewing it and it would really depend on whether or not its “relevant” for them. We don't really need to adjust to spammers and plagiarizers and affect everyone in the forum, they are the ones who need to adjust for us that's why we have a report button and bans in placed for them.