Tesla's stock price is very high right now, largely on the basis that many investors expect it to do well in the future. This high valuation makes it easier for Tesla to raise more money to fund its future ambitions. The short sellers are promoting a story that Tesla will not do well in the future, and is overvalued today. If they manage to convince other investors of this story, the stock price may decline and hinder both Musk's personal wealth and prestige, and Tesla's ability to fund its future operations.

So it's somewhat understandable that Musk doesn't look kindly on the short sellers - he would prefer that skeptics stay quiet and stop trying to ruin his company's valuation. You are correct, however, that acting in a deceiving manner to make the shorts lose money is not an acceptable retaliation.