It's not about meticulously reviewing every commit for every project that I use, obviously nobody has time for that. For me the most important part is being able to fork the project if you want to add features or are unhappy with the way the original project is going, you don't merely have to beg the maintainers to add a certain feature, you can do it yourself. And perhaps more importantly I'm not screwed if, for one reason or an other, the original maintainers decide to drop the project.
It's very important to me that emacs is open source not because I review every single commit (I don't) but because it means that I can commit a lot of time tweaking and learning the ins and outs of the editor without worrying about having to switch to a different one a few years from now when the original devs get acqui-hired by Facebook and they stop working on their project.