More following distance => less throughput. There is already a math problem at play for how to get millions of single occupancy to and from a given location in a day. Which is to say, gridlock occurs today - it is a fact. Increasing following distance by 2 to 5x would potentially be quite bad for otherwise heavy but flowing traffic. Eg: NYC, it is known for good throughput. Light turns green, everyone picks up speed and keeps tight following distances. Anything less and that city would lock up more so than it already does.
Part of the issue is just complexity and variety. 2x following distances on most highways would likely be only a good thing. But in each and every circumstance, not necessarily good, perhaps disaster.
I think it can fun to be the driver that smooths out the shock waves, so I do largely agree with your point. Though, all things being equal, double following distance and that will double the length of a traffic jam. Longer traffic jams are more impactful - it takes longer to get through them & the longer traffic jam distance is more likely to cause back-ups on on-ramps and in turn to the surface streets leading to those on-ramps. Which is to say, a higher prevalence of grid-lock.
The AI crowd is right to say that with 100% AI cars, you can have smooth and fast traffic with impossibly tight following distances. I do believe you need some impractical necessities to accomplish that though.
It’s more effective to let your initial point stand and let the discussion run its course. You’re working against yourself now.