I fail to see the problem with double accounts and why it is a bannable offense. I mean, who cares if someone has two accounts, does this represent a disruption for the forum or something? No, there could possibly even be someone with two accounts both used to contribute positively to the forum. DAs are only a real issue if they are used to disrupt the forum, and in that case people should be banned for forum disruptions not for being a double account.
Besides its complete pointlessness, another problem with this rule is that it favors malicious people over naive ones. In short, it's easier to go undetected as a double account (in fact it's very easy) if you do it intentionally (if you plan it) than if it happens by accident (say a friend of yours comes to your house and creates an account as a joke, you create an account for purely joking purposes). It's definitely one of the most inane rules I've seen online, although it's far from exclusive to this forum. There's nothing inherently wrong with having two or even more accounts.
This is interesting since you have been under suspicion of being a double account.