Obviously I'm not one of the guys you asked, but...
Fish oil is good, though I really don't think you need 40 grams a day (I'm assuming you're not using something like Flameout which would mean you'd need a lot less).
The only reasonable concern that could be raised would be the issue of impurities in the fish oil, things like heavy metals. Taking a bunch of impure fish oil everyday would kind of counter-act the point since you'd be slowly poisoning yourself (to a small, possibly negligible degree, I believe, but poisoning none-the-less). However, I believe Flameout is supposed to be very, very pure and that shouldn't be an issue.
Just because you have an MD doesn't mean you're not dead wrong sometimes.
Hell, they let me into med school.
Also, fuck fish. They're food. Saying that because our ancestors didn't have it we don't need it is fucking stupid too, they also didn't live very long or have shit like MOTHERFUCKIN' PENICILLIN (Link: http://zomgscience.net/wp-content/uploads/2011/04/peni-final.png
So I shouldn't take antibiotics when I get MRSA, right?
As I understood it his point was, after all the other stuff, you need DHA but he didn't want people to get it via live animals, fair enough.
Yes, they suppress the immune system (inflammation), that's a good thing, there are MANY diseases that are inflammation based that kill motherfuckers left and right. So do other COX inhibitors but there's some evidence that they may have preventative effects against CANCER (NSAID use is linked to reduced colon cancer).
They don't thin your blood like fucking Warfarin or anything, either.
As far as being more susceptible to microbes, I'm also calling pure bullshit. I never get sick, I realize that's only one person's empirical evidence, but I never get sick. I down fish oil like they're running out (my shoulders scream at me when I run out).