Most of the vehemence is in regards to privately held companies which can't directly be shorted. In fact, that may actually contribute to the odds of the company being overvalued.
> is definitely overvalued at $80B"
Stocks move in bizarre ways, particularly tech stocks. If you short a stock and time it wrong, you can easily be right about the fundamentals but get killed by the herd in the meantime.Going long is safer, but can still be bad. If the price drops below your buy-in, and a merger is agreed at the low price, you can be forced to sell low. You could have bought into Dell, and then been forced to sell lower than your own valuation.
If you think the market is over-valuing a stock you hold, you sell it. If you think it's worth more, then you keep it, and refuse any offers to purchase it for less than you think it's worth.
These people tried to refuse the offer. As mentioned in the footnotes, only those who voted against the deal were entitled to sue for compensation.