The answer is yes, there is harm. You are harming forum owners and moderators who have to spend time deleting spam users and profiles, and/or spending time/resources installing, creating or modifying software to stop it. Justifying it by saying there are loopholes in some forum software doesn't justify the actions of those using the loopholes to spam. Its like saying someone speeding is only doing it because the car allows them to speed. You are creating pages which takes up unnecessary space in their databases, and adds to the overall bandwidth the site users, however small. You are using someone's else's forum solely for your benefit not theirs. Not everyone in this world starts a forum to learn PHP or anti-spamming techniques... they do it because they are passionate about a certain topic. I've had to go in and clean up this sort of mess and prevent it from happening on forums, and they end up spending money paying someone like me to do it, so there is direct financial harm to those owners.
There will always be folks who will justify a form of spamming, and SEOPTI that's exactly what you are doing. So, while you claim the forum owners are whiners, it seems on the other side of the coin there's some shucking and jiving. On the one hand you say its not spam, then in the last sentence you say it is. This sort of thing adds nothing of value to the forums or its users. If this is the sort of thing you do (for yourself or clients), then IMHO its hardly professional SEO tactics.