It's a discussion forum. It says so here: "Tired after all that DIY? Discuss or debate topical issues here."
The other forums are for DIY advice.
Not according to his profile. Or are you suggesting he's been banned and allowed to return, using the same Gas Safe registration number that he used before when he was banned?
If you are aware of his previous username, perhaps you'll share it with us all, so that we can all know how he helped DIYers, and why he was banned.
You are also suggesting that the other Gas Safe registered people are fully aware of the banned plumbers for being abusive/racist, and welcome them back with open arms.
Which goes back to my suspicion that plumbers seem to feel that they can be abusive/racist with impunity. If/when they are banned, they're welcomed back and consider their abuse/racism all a big joke.
Which would explain why there are a preponderance of abusive/racist plumbers in this GD forum. Some of them Gas Safe registered which potentially brings their profession and the Gas Safe scheme into disrepute. Assumedly, they are using their same Gas Safe registration number over and over again, and are fully supported and defended by other Gas Safe registered plumbers.