As long as honest nodes control the most CPU power on the network, they can generate the longest chain and outpace any attackers.
But they don’t. Bad guys routinely control zombie farms of 100,000 machines or more. People I know who run a blacklist of spam sending zombies tell me they often see a million new zombies a day.
This is the same reason that hashcash can’t work on today’s Internet — the good guys have vastly less computational firepower than the bad guys.
I also have my doubts about other issues, but this one is the killer.
R’s, John