I've been following this thread and one thing becomes more and more clear by the day: 51% attack is truly the doomsday scenario for bitcoin.  There is no solution.

I've read Satoshi Nakamoto's paper and the assumption he makes at the outset is that in the world of bitcoin, a dishonest miner can never and will never obtain more hashing power than a group of honest miners.  He never prepared for the scenario of a 50+% miner on whose honesty we must all depend.  He alludes to the fact that should that happen, bitcoin is doomed.

Let's look at possible solutions:

1.  Let's "convince" all the fellow miners to abandon the pool that is proven to be dishonest....

This goes against human nature.  If you build any system, economic or political where the "greater good" is at conflict with what an individual perceives to be in their immediate interest, the individual's interest will win out.  This is why communism and socialism have failed.  History is full of examples where any attempts to "shame" greedy actors into behaving in socially-centric manner have not had any success.  Humans will only act in socially-centric manner if and only if that action benefits them individually.  Why do you think the US government is borrowing from our children $0.40 for each $1 they spend?  Because our children can't vote them out.

2. Let's provide a technical solution that penalizes pooling. 

So, this will only put the casual miner (like myself) out of business.  We will all be forced to sell our hardware on pennies on the dollar to the "organized miners" who all mine individually but share the same wallet between their 20,000 S1 miners.  Net effect is exactly the same.  There's going to be several such actors and it would be very easy for, say the government of China, to just buy out enough of them to get the 51% control of hashing power.  And, they proceed to destroy the Bitcoin.  I should not single out China here... the US government would do the same in a heartbeat.

3.  There is no 3rd solution.  The miners must follow the longest chain.  If they don't, there will be multiple chains and no one will ever know if their transaction is confirmed.  Longest chain is controlled by anyone who controls 50.1% hashing power.  That actor must be "trusted" to not double-spend.  Regardless of whether destroying bitcoin is or isn't in the best interest of the controller of 50.1% hashing power, the fact we have to trust such an actor is categorically and fundamentally contradictory to the entire premise of bitcoin, whose motto is "trust no one". 

Perhaps smarter people can figure out a solution here, but I just don't see it.