Because it sets a bad precedent and example to the young players in our system. What type of message do you think it sends to guys like Horvat, Baertschi, Etem, Markstrom, McCann, Virtanen, Vey, Hutton, etc., when management deliberately 'tanks' via trade all/most vets? Players aren't stupid.
Establishing the integrity of a team is extremely important. That's how you get the young players to 'buy in' to the team code so that one day, they can become leaders on the team.
So explain what message is sends the youth when you trade one of your hardest working ones away to move up in the draft.
You're in the wrong thread anyway if you want to discuss not tanking.