I find that an invalid argument and would actually say the opposite. Especially because there are counties where they take personal data serious, it's an argument to consider having an account deletion request feature.This can clearly change from country to country so it's best to make this into a mod. Also xenForo is a UK based company so shouldn't it only try to heed to UK's laws or even better USA's laws since it's hosted in USA? Please excuse me as i'm not a legal expertise
Facebook -only- had a soft delete option where your account went inactive; they only recently started testing the hard-delete feature (Don't know if its out yet).If you don't like it, don't enable it!
I would enable this, as it would save me deleting user accounts which seems to be requested every week. Frankly I've got better things to be doing than deleting accounts, and it is functionality offered elsewhere. SMF forums for example have a soft-delete option available to members, as does Facebook.