Will merge mining patch make Bitcoin network mining power available to anyone? I think Namecoin has a good value, but while I think Vladimir overestimates the inflation effect of merged mining, I still mostly agree with his post, which is negative towards uncontrolled merged mining. It requires small patch for bitcoind to make it "parent" for Namecoin blockchain, is the patch exclusive for Namecoin? If yes, what makes it exclusive, and if not, is there a way to design a merge mining patch, so it would be exclusive for a particular blockchain? That way bitcoin community would have a choice, when downloading a new version of bitcoin, if it wants to adopt a new blockchain.
The patch has no effect on the parent blockchain, it just allows the patched bitcoind to be used for mining on both chains simultaneously.  Only the child blockchain needs to be modified in order to support merged mining.  There's no way for the Bitcoin network to prevent merged mining, even if doing so were desirable.

Merged mining does have to potential to allow alternate chains access to greater hash power (and thus security against double-spend attacks) than they would have had otherwise.  However, this alone will not give them value as currency.

Bitcoin is able to sustain value because of its network effect.  The more active users it has, the more useful it is to each user.  The alternate blockchains have userbases that are a a few orders of magnitude smaller than Bitcoin's.  Newcomers to the cryptocurrency world will tend to choose the more useful and popular chain, further increasing Bitcoin's lead.