He could have said "no thanks", when they approached him.
It's a bit like cheating on your mrs because some stunner came on to you. You wouldn't say she's disgraceful when you're the one dictating the game. Yes it's a dirty tactic, but it weeds out the rats. Would you rather he carried on doing this behind closed doors?
What is it exactly that you and others think he did that was wrong? Also what was behind closed doors? It was a meeting and afaik he stated that he would only accept the role if the FA gave their permission.
He's pretty much been fired because people don't get that people in positions of power with contacts and influence extremely commonly get paid to essentially be an advisor in situations like these. Getting 'around' third party ownership isn't really, a thing, nor against the rules. The general idea was pump up a players value and make a big pay off with their final move when third party ownership is terminated. Now instead of that, effectively they work as super agents and take a larger than normal fee with the pay off for the player being a agent with more access, more influence and the ability to then get a better deal at a bigger club for the player that agrees.
It's less like cheating on your wife with a stunner, and being in an open relationship, sleeping with a new woman, people not knowing you're in an open relationship and jumping to conclusions that what you are doing must be wrong because without knowing everything it looks like it's wrong.
In effect, agents are third party owners, maybe so are managers, always have been and continue to be. It's just become about getting the profit from the entire career of a players wages rather than building up to a single transfer.
This whole thing appears to be mostly the wording of what he said and most people not understanding that it wasn't breaking any rules and that probably the massive majority of people in his position taking similar roles.