Labeling trades involving draft picks as something you shouldnt' do is way over-simplifying everything. Each trade should be taken as an independent instance in and of itself. After that, if you want to put together trends, it makes sense to do so.
If Marv gets a productive player for each pick he trades away, how can you complain about that? A 5th rounder for Hargrove, in and of itself, seems like a very good move to make.