You make a valid point, but I personally don't consider that tanking. At some point in a season (often the trade deadline) it often makes sense to sell off short term assets for long term assets to help the rebuild. As you indicated this sometimes results in a bottoming out, but it has been known to improve the competitive advantage of a team if they have NHL ready or close to NHL players in the system.
Very true and maybe using the "short term assets" was wrong on my part because it would be imprudent not to get value for those players. In general though GM's of non contenders sell of players whether it be a short term asset or longer term ones for futures. I think we'd be naive to think that they don't take into account the impact this could have on their draft spot along with getting the futures.