Vance Lucas has tossed his hat into the ring in the debate about private versus protected scope in PHP projects with this new post to his blog.

The age old private vs protected debate has been re-ignited in the PHP community recently following the decision of Doctrine2 and Symfony2 to make all class methods private until there is a very clear and proven reason to change them to protected or public. The intention is a good one - to ensure they are providing a clear and stable API through intentional and known extension points that they can better test and support. [...] The problem is that this kind of thinking is a slippery slope that kills the spirit of programming.

He suggests that, by limiting the scoping down to private, you're taking away the very thing that gets most people excited about third-party tools - the extensibility. In his opinion, it sends a strong message to other developers that they're "not welcome" to make suggestions or updates to the application/tool.