Richard Stallman is one of the main authorities regarding the open source software movement. Even though he may tend towards leftist politics, his page is still one of the best sources to go to regarding questions in free software and sometimes also about politics.
I did not really know how to cagegorize his homepage, since it is not just a blog, but it put it into blogs, because it is mostly a blog, but I can also recommend the other categories at the top, especially the list of "What's bad about:" since there he explains what is bad about each of those things and my recommendation is, you should not use any of those things that he lists there and if you want to know the reason, you can click on each entry, there he will provide reasons why not. One of the main reasons of course is always "requires the use of nonfree software" but the other reasons and reference links are often helpful to debate with other people.
With the political activism you have to be a bit careful and think for courself, because leftist political activism is no longer what it used to be, but I always like to use Stallman as an authoritative reference to debate with leftists about open source related topics, because they should accept him as an authority at least partly, even though they often deny it, if they lose the debate with me.
So in short Stallman is an essential bookmark to keep as reference for open source related topics.