In general I'm neutral about tanking, but some situations are to be avoided.
For example, I'm contending the league with another team (3 points below me) and tomorrow we´ll play against in the last game of the season.
Today I'll play agains an inferior team and my rival against a tanker (129%).... who decided not to tank in this match! I'll win easily both game with this tanker due to those silly formation, but my rival won't have the same treatment. That's totally unfair! If you want to tank, ok, but must treat the same way all the players...