There is much to be said for the merits of trials. Trials are public displays of the "process" of "due process" being applied to the merits of a particular case, in a public forum that is both transparent and based on objective standards.
There are two glaring problems: substantive, and procedural. They are of equal importance. Without hard and fast terms as to each, you're not holding a trial. Rather, you're holding a kangaroo court.
Substance. The substantive problems begin with our shared uncertainty -- assuming we're all humble enough to know what we don't know -- as to what "rule" was actually violated. The Terms of Use, or whatever they're called here, aren't really "a proscription of law" so much as a "set of generalities" that make almost no reference to specifically forbidden conduct. This matters because we abhor ex post facto rules/laws/etc., which is to say, we do not write the rules that apply to a particular case after the fact. There are some countries in the world that do that, but no country in the West does. Given who we are, it would be inconsistent with any notion of fairness to come up with a standard after any member has already done something seemingly objectionable, and then put them on trial for violating the standard we only came up with after the fact. Given that now (and, by implication, after the fact of the occurrence) we would have no choice *but* to do that, a trial for anything that's already happened would be out of the question.
Procedure. The procedural problems begin with what I would hope would be an almost universal recognition that there is no established procedure for what constitutes a fair trial in the context of, say, a site like DDO or DA. In the US, for example, we have an adversarial system where a prosecutor has the sole burden of proof, the defense has no burden, and a judge "calls balls and strikes" as the procession unfolds. A jury of an appropriate number of people typically decide such matters. There is a formalized structure for who can talk (attorneys and witnesses), who can't talk (the public), what can be said (rules of evidence ensure that unfairly prejudicial material can't be used to corrupt the process), who can decide (a neutral jury free of bises, and personal or other conflicts of interest) and the like. In a criminal context, a trial follows a lengthy investigation that, too, is governed by all kinds of rules and procedures.
Here, or anywhere on the internet, I don't know how we could ever have anything approximating a "fair" procedure for "an accused" (that is, even if we weren't writing ex post facto rules). To keep it simple, let's start with trying to set up something like an adversarial scheme of prosecutor and defense. Who is in a fair position to prosecute? Who is in a fair position to defend? Almost no one, because any prosecutor is likely to have a personal relationship with the accused. This is less a concern with the defense, but the point remains. Now, what about the jury? Who will be neutral *enough* that any decision they rendered wouldn't at the very least appear to be blighted by personal biases? Given the small userbase and the fact that most everyone is at least familiar with most everyone else, there doesn't seem to be enough people to support such a process with any legitimacy.
There's something else to chew on, too, which is the "rules of evidence". Now, laying aside the fact that we don't have any rules of evidence, let's just begin from the basic premise that there are some evidentiary items that are not fair to introduce. One example of such items would be those which are inflammatory, whether relevant or irrelevant. Here, where you have a user that has a noted history of conflict which goes well beyond the specific 'charge' on which he would be tried, would it be fair to present a "jury" with something approaching a 'parade of horribles' as to the character of the accused? No, it would not, because we don't punish people for their character in fair legal systems; we only punish them for specific violations of law. Even assuming we had such a set of rules in place to prevent that kind of abuse, most jurors would be independently aware of those facts that shouldn't have been admitted into evidence anyway. What's to stop them from making a decision on that basis?
This brings us to a final procedural element, which would regard sentencing. The "and should be banned" language I have a real problem with, because I have no idea what it means. Banned from the site, forever? Banned for 24 hours? Banned for 5 minutes? Banned only as to this account but may create another? Totally vague, and ambiguous. But, even that notwithstanding, what juries primarily do (there are exceptions, like in death penalty cases, which raise their own issues beyond the scope of my point here) is "find facts" and announce a verdict. Juries generally don't sentence offenders, unless we're deciding whether the state should murder someone. Community decided sanctions lend themselves to all kinds of problems, especially given that we've got no way to keep unfairly prejudicial material out of the process.
This is only like... the most basic set of concerns, discussed on an incredibly superficial level. Given this, though, it's certainly enough for any reasonable person to reach the conclusion that, if these concerns are applied to the specific case of whatever RM did to deserve this most recent ban, there is no way to even begin to set about trying him fairly. Does this mean that mods are a better alternative? No... of course not, but that's of peripheral concern to me.