Well.. that's were you err. It's on you to prove to the deciding instance that a change would be good. You are the one intent on changing things. You are the one that needs to prove it would be beneficial for the server. The arguments you brought up so far do not persuade and run contrary to what we try to achieve on a general level. I also think the reasons you were provided so far, by myself and others, are quite sufficient to justify the current rules. And just now, Myrdraal gave a very convincing example of why there is little appetite on our part to move in that direction.
Because some other combos are currently busted is not an excuse to allow more busted combos. Balance can, and absolutely should (in my book), be achieved by toning down what is too powerful, not in an arms race to empower classes that are already strong on their own.
We're not even in a debate at all here. There is none to be had. You made a fair request to change a given situation. I'm not faulting you for suggesting it. But you were given the reasons why it won't be, and now comes the time where you must accept the decision and move on.
I have not made any request in this thread actually. I merely took the opportunity to expose my viewpoint on the subject, which happens to be favorable to allowing paladins to multiclass. To which you have responded. As I saw your point on balance, which I disagreed with, I chose to address it as well. You answered saying I was not debating productively. Now you are saying we are actually not in a debate at all. If you would make up your mind, then I would have an easier time responding to you in kind.
The server rules are for the staff to decide, and you are free to disagree with players when they criticize said rules, and if a player's request gets declined, there comes a point where they have to accept it and move on indeed. But if you engage in debate well... debate is a multiple way street. It's not for one party to convince the others, but for all engaging parties to expose their viewpoints and respond to each other's viewpoints. At the end of the day, some may change their minds, often no one does, but that is how debates go.
As for the example provided by Myrdraal, it is easily addressed by making paladin require a minimum of 5 class levels. There would then be very little that a paladin would be able to achieve that a blackguard couldn't.