...They don't even have to provide much (or at all) financial incentive for miners, as for them there is no downside in adding another blockchain to hash. It only needs to be for something a big part of miners would support for one reason or another, and you get your hashing power.see no problem with that....
meeeh... wrong answer . No.hashing.power if incentives <= 0
everyone is free to have it's own block-chain. I would definitely
not mine 10% or less of my total hashing power for another block-chain if that percentage it's not equal in price with the main block-chain. Actually I'm free to mine namecoins if I want to support distributed DNS, which I do, but my incentives are low for the moment. Namecoin will have to make it's way like bitcoin did, slowly, gaining it's users trust and no free hash power. It has the same security as bitcoin, don't need to worry bout it being fragile. Just my opinion.