Although I've been inactive for a while, as a moderator I feel the need to throw in my 2 cents.
For years the forums have been moderated in a fashion of minimum effort, with pretty much all major action such as topic deletion/locking and user banning being motivated by spamming, warez or anything else that clearly has no place on this forum content-wise. I can also recall at least one case of a user spinning into such excessive abuse that he got himself banned (names are withheld to protect the stupid) but that was after repeated warnings during a prolongued period of weeks that he set out to not just derail topics and flame others but descend into pure abuse on both the forums and other IV-related community platforms. A third case (mostly pertaining to topic locking) is limited to bug reporting forums, where occasionally people (including yours truly) set out to arrange the chaos into something slightly more orderly. This, however, is where the forums are not really used as a traditional BB so it's hardly applicable to the forums as a whole; I included it to show just how particular the circumstances have to be for the moderators to feel like stepping in.
Having said that, the Defcon forums suffer from a reputation problem. With all due respect to the therein active community members, it is really a separate part of the forums and one that I have always been very clear about not setting foot in as a moderator because I don't feel the slightest bit motivated to dig through some of the bullshit that happens over there (admittedly I'm not being overly objective here, but to be fair what you are reporting here is precisely the kind of stuff that many feel could only happen in the Defcon forums). I mostly felt comfortable stating this disposition because there were some other moderators around at that time who happened to be active Defcon players and so were visting the Defcon forums regularly anyway. Over the years they (like me) gradually phased out their activity over here so there was a need for new moderators, and the combination of the forums reputation and the fact that it is a very active community on its own, preference has in recent years gone to forum-specific moderators picked from those same forums rather than (like bert and I are) general moderators.
The fact that I have rarely set foot in the Defcon forums post-beta also means I have difficulty assessing the situation and judging who or what is behaving unfair. Since the Defcon forums are really regarded as a quite separate part of the forums, with their own active core that has very little overlap with the rest of the forums (indeed, Defcon's target audience has very little overlap with IV's traditional target audiences), I would not be surprised if it needs a bit of a departure from the traditional laissez-faire mentality that we use in the other parts of the forums. The Defcon crowd simply has more problems with pouting abusive teenagers than e.g. Uplink and Multiwinia, and it has a slight tendency to take the self-ruling part to the more negative side of anarchy. Even then, though, user bans should still be considered a last resort, only ever used when well-founded and most of all discussed with other moderators before execution (and if a user is a repeat offender, every single ban should be proposed anew for discussion within the moderator team). Such a mentality would prevent situations such as this where a moderator is being accused of partiality: either the ban is not executed because no moderators agree, in which case the community is left to its own devices to handle the situation, or the ban is executed but there is a clear signal that multiple moderators agree so there is no reason to assume there were 'unprofessional' reasons.
With this Introversion Moderating 101 in the back of our heads, I think the stuff that is being said here should at least require an objective third-party look. Again, I'm considering two potential outcomes: either someone has been abusing moderating powers and that needs to be addressed, or the moderation is considered justified but the community needs to be given better justification for it.
My personal recommendation is that you try to put together a timeline of how events unfolded (with links to topics in question) and send them to one of the ohter moderators. Initially I would advise you to contact one of the more active moderators (I've been away for a while so am even less informed about the state of affairs Defcon-wise than usual) but if all else fails, feel free to send me a PM and I will look it over (and if I think there's enough in there to take action, I'll discuss that with the other moderators and admins).