The 51% attack would require large hashing power, which would be very difficult on many coin (scrypt and x11) so basically that would work only on coin which aren't popular and are not a danger to altcoin.
The real danger comes from all the IPO/pyramidal schemes which are now launched on a daily basis and most of the time and there isn't much which can be done as the btc are "invested" prior to the launch of the coin.
Considering incentive to short a coin, good but who would pay for it ?
And who would decide if a coin is good or not ?
And what would prevent generalization of attack between coins, blackmail, corruption, etc...
The main problem at the moment is that many of the new comers don't care at all, it wasn't like that when I started (and it was less than a year ago...) when people didn't like the crap some dev was putting, they were complaining and moving on. Now absolutely everything has became acceptable.
I already spent too much time on some obvious scams, telling people it was an obvious scam, nobody gives a shit...
while they are likely to loose their money... That's pathetic.
The problem is also some big players which are clearly organizing (or actively participating in) those scam and without their agreement any regulation won't be impossible.
Trying to ask the Mafia to regulate the crime market would be easier...