I don't oppose it because it alters the balance of power, although I understand how the quote you are replying to could read that way. I oppose it because it alters the fundamental nature of the competition. Two teams enter the season with the assumption that they will have to compete for a playoff spot by facing 13 teams who are trying to win. Instead, one team has to face 13 teams trying to win, the other team has to face 12 teams trying to win and 1 team trying to lose. The nature of the competition has been altered, and the competitive landscape has shifted.As for "It alters the competitive landscape and imposes negative externalities with no positive externalities to offset." The competitive balance piece of that is not a convincing argument. Lots of totally acceptable strategies alter the competitive landscape. That's not a prima facie argument against tanking. The negative externalities piece is legit, although my personal opinion is it's being overstated. That said, the extent to which tanking generates negative externalities is totally subjective and will vary from person to person and league to league.
I don't oppose all things that alter the competitive landscape as a matter of course, but my default is to oppose them, and in order for me to overrule my default, there must be some net benefit to the league as a whole. Tanking provides no such net benefit.
As an example of a change to the competitive landscape that I would be in favor of... if the league's teams all unanimously approve of a rule change that goes into effect during the middle of the season, then that changes the nature of the competition, but also provides a net positive benefit for every team (or else the 12 teams wouldn't have unanimously approved it). So sure, in this case, feel free to alter the nature of the competition halfway through the year. And if the entire league votes to approve tanking (or if the entire league approves a voting system whereby rules can be created or changed without unanimous approval, and support for tanking meets the pre-decided level of approval), then sure, tank to your heart's content, and good on you for doing so.