That's true.
But IMO, to make it worthwhile, you still have to get the timing right. That's the hard part.
Identifying a bubble is relatively easy. What you don't know is how big it'll get and when it'll pop.
Definitely a ripe spot for put options... but there are no public put/call options available for LNKD yet, as far as I know. It's impossible to price an option without having some history of the underlying security's volatility--and we have zero history for LNKD.
The spread would have to be gigantic to lure market makers into such a trade--and, rightly so, investors aren't interested in gigantic spreads.
If you want to get bearish on this you'll have to strap on your helmet and just short it.
This is what put options are for.