Administration set the rule "joining RDF only to idle and refuse to leave on your own to avoid the debuff.". Don't idle around, with your big brain ideas. Easy.
Oh and in your story, 1 guy went to continue towards completing dungeon and you went towards some optional boss. What did the other 3 do? bet they went with the first guy, but you needed written statement from them or something.
They waited and when he did not come back, they followed him. perhaps they simply did not want to deal with the situation. but I wanted to. I proposed a completely fair solution. it is the same for me and for him. We both can win or lose and have no influence on it. but I was denied even this and in the end I also turned out to be wrong. looks like discrimination, which, by the way, is prohibited by the rules, and here you support and justify it in every possible way.
It is something specific. When you join trough DF, goal is to complete the dungeon, condition is set by the DF system. Everything else is "something specific".
You did not reach agreement, so it defaulted to default agreement, which is to complete the dungeon.
Find people why want the same things an do it.
No, mathematically you get more eot by breezing though dungeons via DF tool, skipping mostly everything that's skippable.
They made their choice. Not agreeing with you is not a discrimination. No one has to listen to what you say or want, it is completely with their right to ignore everything you say, why should they give a **** what you want? They just want to complete the dungeon(which you stated as your own goal also, by joining trough DF tool, btw).
This is how legislation works: if something is not prohibited, then it is allowed. If the law does not describe the situation completely, then it can be interpreted in a way that is convenient for me.
Likewise, GMs can suspend players under their own interpretation of the rules. Do not use real-life law for comparison with a private server rules. The GM has the final word on it. Of course, you can appeal a ban if it can be applied, and support will revise and see if you may be forgiven.