#1: Already stated I don't have hard proof, but I want you to prove to me that +5million WoW players use addons. I still believe in my first point but we'll follow court rules and say the point is tossed due to lack of proof. Lets look at the others, shall we?
#2: Fallacy? Raiding guilds all require at least a DBM equivilent, some require more. Allowing addons to TOR will bring similar functions and the same results. Saying players don't have to use addons then requiring them to raid is an invalid argument. (I'm not saying its better for the raiding community. I'm saying the argument itself is invalid)
#3: Check the MANY posts on these forums from people stating the exact thing that a lack of DPS meters and the like will keep bad players hidden and able to stay bad. People are making the argument.
#1 burden of proof fallacy, here we go again. But yes, let's turn this one over for now.
#2 the slippery slope fallacy here consists in you stating that IF addons are added, they WILL (necessarily) become needed for raiding. This is unsubstantiated. Look up the problem of induction if you're thinking about replying "but WoW has shown us [...]".
#3 the argument I see people making, which in wording resembles yours, is that of assigning a motive to the people not wanting addons of wanting to have their "bad" stay hidden. This is different from what you are writing, in that this argument never assumes that bad people want to improve, but merely that they don't want to be criticized by other people. Of course someone who wants to stay bad can do so, but whether he can get away with it or not is another matter.