It is not that hard to restrict the buying/selling activities. True that you can't stop it completely, but depending on what the community wants, you can restrict it.
I don't personally appreciate buying accounts for participating in campaigns and making lot of posts though not actually interested in discussion. Kind of reduces quality of the forum.
On the other hand, there will be less activity, and accounts will be valued less, collateral issues, etc. will come about.
I'd say leave it to the community to decide. (as it is already)
But it is possible to restrict that. Take action on buying/selling account threads, and restrict a bitcointalk account to a single non-changeable email account. Make resetting password through email the only available option.

(I think the security question should be removed for good. It makes accounts too vulnerable)