The problem with open source is not that the source is available, that you can modify it to your own needs, or that you can contribute back, it is that anyone can redistribute your software for free, and that you can't discriminate between e.g. small businesses or personal use and Google in your license terms. This cuts off the possibility of actually supporting yourself financially as an open source developer in many cases and is an ideological commitment that mostly benefits large corporations at the expense of individual developers.