As open source project evolves, it will attract more contributors into the project development. They can help to improve the code to make it more efficient and perhaps adding new features along the way.  However, with more contributors, conflicts will also arise because human beings can't always agree with each other -- especially when the group gets larger.

In other open source projects, groups can resolve disagreement with new project fork and carry on with the development in separate ways.  However, in the case of Bitcoin, such fork may be fatal to the survival of the Bitcoin ecosystem.  

Let me illustrate my point with a hypothetical scenario: "A group of developer wants to change the rule of Bitcoin network to allow old coins that have not been transacted/circulated for x number of years to be recycled as mining reward in future blocks.  A vote is conducted and 40% of the active Bitcoin users is in favor of this idea. A fork is done, with 60% of the miner staying with the original Bitcoin project, and 40% of the miners move on to the new fork".

Unlike project forks that restart the blockchain, such as Litecoin and Bytecoin, the fork that resulted from this hypothetical scenario will likely continue with the current blockchain.  In the short term, many of the users with bitcoins in their wallet might not even reject such fork, as their wealth have seemingly doubled with their coins appearing in both the blockchain.  However, in reality, the network security for both the branches have been severely weaken, making them more vulnerable to 51% attack, which may then result in downward spiral for bitcoiners to lose confident in the system.
 
Applying Prisoner's Dilemma,  these two groups might not cooperate, even if it is in their best interests to do so (i.e. not to fork). The 0.7/0.8 fork issue was resolved quickly because majority of the people agreed to cooperate.  But there will likely be more decisions to be made in the future, and we can't be sure how groups of people will react the next time.

The possibility of a future project fork, is like knowing that there is a bomb in the system but you have no ability to disarm.  

If democracy is what made Bitcoin successful today, it will also be the same democracy that kills Bitcoin in the future.