He's giving his opinion based on his life experience and research, and you have a contrary opinion based upon your life experience and research. I think that's all fair game in a civil discussion. Houndoc could very easily post videos of Fauci or any other medical professional that disagrees with this Dr, and since you disagree with that, is it fair for him to ask you to compare your credentials to theirs?
As you are very quick to point out, just because a dr says it, doesn't necessarily make it true. I'm sure there are other Dr's and medical industry professionals that are on record saying something very contrary to the Dr in that video. I don't think it's an absolute...either one is right or the other. I think the truth lies somewhere in the middle, and we are able to use our background, experience, opinions, training, research, or wife's cousin's boyfriend's friend's opinion to make up our own conclusions. But now matter how much we believe in our own opinions here, none of us 'know', you know?