Yeah the use of SWIM grates on me tbh. It makes threads/posts hard to read and thus makes me less inclined to read on and help out. That said, I don't think people use it because they think it'll actually provide them with any form of legal anonymity - they do so because most other drug forums that they've frequented in the past require them to do so, and so just assume the same applies to BL.
However, once it's pointed out to them by either a mod or member, they usually apologise and correct their post quite quickly. The mods are usually very quick to clamp down on its use and you can guarantee that within the first 2/3 posts of a newly created thread, either a mod or member will politely remind them that the use of SWIM is not permitted on BL and to have a quick read up on the rules.
It's not like new members are using it and mods are sitting back and doing nothing about it - they're usually very hot on their tail to eradicate its use - as they are with drug testing threads - which is also a repeat offender. Some mods even go to the trouble of editing new member's entire threads and replacing SWIM for them, and then politely remind them that its use is forbidden and directing them to the site rules. Which is very kind of them, considering that they could just post saying 'no swim - read the rules' and close their thread.
I think mods, and members too, are already putting a lot of effort into eliminating SWIM, I don't think there's much more BL could do. I don't mean to be patronising, but if you have any ideas yourself that could help stop its use, I'm sure the mods would be open to suggestions? The only thing I can think of to eliminate it completely is having every new thread reviewed by a mod before submission, which just isn't viable.
I agree it sucks, but I think mods & members are already doing a great job to eradicate it - and I can't see a viable solution as to how it can be completely eliminated.