There are two main reasons why we haven't implemented a feature that requires approval of new members' posts. First, we don't have the manpower to review that many posts. There are about 800,000 legitimate posts on the site (ie, deleted posts excluded) that were one of the first two posts made by a member. At current posting rates, we would need to manually review about 300 posts a day. The moderators and administrators are all volunteers, so this would not be feasible or fair.
Second, we prefer to avoid measures that inconvenience regular members. This would, since there would be a delay between when new members post, and when the post becomes visible to other members, making it harder for them to participate in conversations or get help with problems they are having. This is especially true since the large number of posts that would need to be reviewed would mean that there could potentially be quite a long delay before they were approved in some cases.
We do have a range of techniques that we use to reduce spam or stop you seeing it, and we're constantly working to improve them. It's a bit of a cat and mouse game though, and spammers often find ways to circumvent restrictions we put in place. For example, if we require the first one or two posts of each new member to be approved by a moderator, spammers will learn to make some legitimate looking posts, get them approved, and then post their spam. And if we limit how often members can make new threads, spammers will instead post their spam in existing threads, which is harder to spot and remove.
We do welcome feedback though, and are always happy to hear new ideas.
