While the distinction between actions that are against the rules and tanking, which technically isn't, stands, I don't really think the analogy to three-point/passing strategy is a particularly good one. In that analogy, you're comparing actions that teams take to get a competitive edge on a game-by-game basis with actively shunning the competitive edge on a game-by-game basis in the hopes of a long-term competitive edge. Many fans - I'd say probably most, though certainly not all - see a big difference between trying to win at all times, and trying to lose now in the hopes of trying to win later.
Maybe it's not against the rules, but it leaves a bad taste in a lot of fans' mouths in the same way that cheating does. On the other hand, I can only think of one person I've ever known who might say that a team actively shooting more threes to try to win is worse or even on par with tanking, and Slim is a different kind of guy.