Just speaking for myself, I find it disappointing.
When faced with material that breaches the rules, you can ban the poster (temp or perm), lock the thread so it drifts away but people can at least see why it was locked, or delete the entire thread.
The last option is most offensive to me, and I'd hope you reconsider this policy. Not only does it mean that posters who gave genuine non-rule breaking posts have their time and effort destroyed unfairly, but it also engenders a 'them against us' atmosphere and a 'why do I bother' attitude. If I see a thread with a pic of a c@ck, and it is locked and the poster is banned, I think fair enough, the poster knew what he was doing, Mods doing their job well, and I think most would think the same. If the thread is gone and I see no evidence, I'm left to make a conclusion about the Mods who have just unfairly deleted posts I spent time on. Needless to say, the Mods do not look good in this light. I'm reminded of the childhood days when I used to get class detention almost every day, just for being in the worst class in the school. Never respected it, never respected those that enforced it.
Your choice of course, but if you're going to refuse to delete posts that the users themselves want deleted, and yet happily delete posts that the users spent time on and want to remain, you are now giving double the reasons not to post anything at all.