"We should be able to argue respectfully on the merits of the facts, or just cordially say you are not interested in engaging in the discussion."
Again, this isn't the point. There is no need for a cordial expression of disinterest, when it is abundantly clear, based on the context alone, that this was an entirely unwelcome discussion even before your brother pressed send on his very first comment. You're more than welcome to engage in this debate elsewhere, but here and now is not the place or time for it. With all due respect, this should have been a very elementary exercise of reading the room from the beginning. I loathe that I'm even engaging in this by responding, but the lack of respect and human decency is mind-blowing.