No, the problem is that the LC-MS has - at various times and in numerous ways - officially and with great vigor declared the ELCA (and the LCA and ALC before it) as "heterodox," non-Lutheran and sometimes worse.
So the die is cast. No "loyal" LC-MS member can begin with any other premise but that we in the ELCA are wrong and non-Lutheran. And we in the ELCA would then have to prove to you that we are not wrong, which is the wrong way to foster dialogue.
That simply makes no sense, unless one subscribes to the nonsense that multiple contrary things can all be simultaneously correct.
The only "dialogue" that makes sense between different bodies of Christians is either to discuss what things they can do together that do not require either side to abandon beliefs it holds as being defining truths, or to discuss their differences with the understanding that each side is going to attempt to persuade the other side to change it's mind.
Given that you can't even define "Lutheran" beyond "Anyone who says he's a Lutheran is a Lutheran", which is pure poppycock, of course you're going to get in high dudgeon if someone says that because you do not conform to the definition of what a Lutheran is, that means you are not a Lutheran.
If you say that you are duck, yet you have no feathers, no bill, no webbed feet, no wings, and cannot swim, fly, or quack, then you have no reason to be offended if someone says you are not a duck. So why do you get offended if the ELCA does not conform to the definition of a Lutheran church body, but simply says that it is Lutheran?
What proof or evidence can you present, other than self-claims, that the ELCA is currently a genuine Lutheran church body?