It's not an inevitable law of human society that if a group is unfairly attacked by some party cannot then go on to unfairly attack someone else. While it's easy to think of victimhood and especially one's own victimhood as an attribute, it's really a transitive relationship.
Not to say which of the FSF or Cannonical is right in this dispute, I'm not sure myself, but this article made a seriously problematic argument.
I don't think of myself as a victim here. Indeed, Microsoft's attacks back in 2001 drove me to work hard and learn how to run a non-profit in a time when it's constantly under political attack. This has served me very well, and I use it today when my current org (Software Freedom Conservancy) is attacked for its GPL enforcement work constantly.
Canonical, Ltd.'s attacks are more of the same. My blog post is about how Canonical really is just coming after the same group of people that Microsoft once was. I don't feel I'm a victim of either entity or any of the individuals involved. By contrast, they are my political rivals bent in doggedly pursuing their political agenda while I pursue mine. That's an overly Hegelian analysis of the situation, but hopefully that gives a flavor of what I'm thinking about in juxtaposing the two events politically.
May I suggest that there's a big difference between being called the Devil, and being called a witch hunter after you accuse someone else of being the Devil? I presume that when Microsoft called the FSF a cancer you didn't just sit there but made counter-claims about why Microsoft was saying that, right?
I do think that Canonical was in the wrong on this particular issue, but there's a big difference between someone who is a serious enemy of your organization, and someone who is just hurt due to the mean (if more or less justified) things you said about them and is lashing out based on that.
I don't think that post makes the argument you're objecting to. The author was just noting that advocacy for the GPL's version of "software freedom" has been attacked in the past by Microsoft and in the present by Canonical using oddly symmetrical language.