Also note that eventhough Clam is currently in constant 51% attack vulnerability the likelihood of a 51% attack is much lower than bitcoin as the custodian would harm himself the most of all by destroying this coin where his whole business depends on. Bitcoin however, due to it's high market cap and visibility, has many enemies that could easily invest 100 million in mining equipment or threaten a few mining operators to do a successful 51% attack.
Not so - an exchange does not depend on one coin to run it's business; they typically have 10s of coins open for trading. In addition, as I mention below, the shorting attack can make this cost free.
This however I don't see as a big problem. It's inherent to high security, that once it does break, you're fucked. The problem is that bitcoin has way too low security. You only need, not min 51%, but max 5% of the coins in bitcoin (and liquidate them for mining equipment) to do a successful 51% attack.
In bitcoin you need a continuous investment of
25 BTC per block in order to attack the chain. That's $1,605,600 per day at current prices. And as I've already explained, the shorting attack in POS makes attacking a POS chain cost free.
I can't follow your reasoning here but I do know that to short you need the coins as well. Who is going to lend you 5%, let alone 20% of the coins? Extremely unlikely.
Yet entirely possible.
Nice theory but in practice NXT, the first 100% proof of stake coin is rolling for 2 years now and a 51% attack has not even come close to success. In the meantime many other Proof of Work coins have been attacked successfully and even bitcoin is in dire straits.
The absence of a thing does not prove anything. Theory matters. A lot.