I think the general reason why the site prefers to vet new applicants by approving their first few comments is precisely to avoid the dreadful unpleasantness of having to actually ban anyone. Other sites may have the attitude that using the ban hammer is best for all, but I've been on both kinds now and greatly prefer this system - taxing though it may be on those who are charged with the responsibility of having to vet all the new comments from all the new applicants. I think it makes for a much nicer atmosphere overall.