It really depends on what the goal is. Do you want to win a championship or just be a team that makes the playoffs.
If making the playoffs is the end game, then tanking is not necessary, we can re-tool the roster make some key trades or free-agent signings and get that 4th- 8th seed in the East.
However, if the goal is to win a championship, I believe it is absolutely necessary to tank. Here is why. Tanking ensures a greater chance at drafting future super-stars (granted it is just a "chance") and at the end of the day you need super-stars to win or rather, MVPs. Going back to the last 30 years, only 3 teams (Detroit 89,90, 2003) have won without a soon to be MVP, current, or past MVP. At the end of the day, history has shown that you need extraordinary players to win an NBA championship. Now there have been some teams that have been able to sign MVPs via free agency or through trades (Sixers- Moses Malone, Lakers-Kareem Shaq, Miami- Shaq Lebron), however, right now I don't believe Toronto has developed the sort of reputation to acquire MVP type talent. This is why I believe if the goal is to win a championship, we have to tank and hope to draft that future MVP.