Requiring membership before posting is a feature of most worthwhile forum software as it is of IPB used here. Those that don't tend to be even more plagued with irrelevant spam than we are.
Removing this feature isn't practicable, even if we wanted to.
Removing posts or memberships on request aren't things that we do either, partly because it's closing the door after the horse has bolted. This is the internet and anything you posted here will probably have been spidered many times by now.