If you short a company valued at $50B, with 5% of your portfolio, it would have to become a trillion dollar company before you go insolvent.
If that's still too scary for you, you can short it with 1% of your portfolio. Now the company needs to become a $5T company, before you go insolvent.
If you honestly think that Tesla will surge into a $5T company, before crashing back down to <<$50B, then you're the one living in a reality distortion field.
If you claim to be extremely confident about Tesla's stock crashing, but aren't willing to take even a 1% short position, then your actions don't match up to your words.
Did you short Monsanto in 2015 because you expected Roundup lawsuits to hit the stock? Well, you were kind of right but that's Bayer's problem now. Monsanto (the stock MON) is no more and you position was closed at a loss.
If being 15% short is a not-so-good idea, that’s the situation now for people who entered a 5% nothing-to-worry-about short a few months ago.
Should it triple again in the near future, the short would be 45% of the long position (and they would be sitting on a huge unrealized loss).
Being right in the long term is not necessarily enough for a short to be a good investment.