When you plan an IT infrastructure's capacity, you never use more than 30% of its planned capacity, because you must leave lots of room for emergencies. So if average home bandwidth limit allow you to run 8MB blocks, then 2MB blocks will leave you enough room to deal with emergency situation where bandwidth suddenly dropped due to unforeseeable events (I still remember that during 2007 under sea fiber optic cables incident, there was almost no way that you can connect to Taiwan and Chinese mainland network in any speed higher than 56k dial up)
I see your point.
I would like to define Bitcoin first as precisely as possible. Attention to details here is crucial.
Bitcoin was created as a "single PoW-secured transparent unified ledger runnable by users at home".
That's the niche it came here to fill and that's what it's known and valued for. This has proven itself to work.
Now, with technology constantly improving itself that niche continues to grow, while Bitcoin has approached its temporary limit.
We need to find a right balance between the two opposites here.
If we over-protect ourselves and let the gap between Bitcoin's current capacity and that of the home-based internet infrastructure grow too big,
the competition will take the chance and begin filling that niche not leaving any empty space for Bitcoin to grow further. That's where Bitcoin's game turns bleak.
If we, on the other hand, relax the idea of the limit by removing it altogether (or hooking it to the exponent), we might shift the incentives structure to the point, that the network will begin consolidating around high-bandwidth lanes, leaving the home-based demographic out of the picture. That's where Bitcoin stops being itself.
If we show ourselves undecided either way, chances are, that the network will split itself into two extremes outlined above and Bitcoin will have to accept a technical defeat. That's why Chess has a clock. Stall for too long and the game is over.
So, if it's shown that 8MB is a reasonable limit to satisfy the conditions above for the next 4-6 years, I argue, that we shouldn't target anything less.
The idea that global internet infrastructure might suddenly shrink is theoretically possible, but since we are targeting home internet connections here, I'm almost certain that 8MB should be workable across the ocean at any given moment. If it isn't (workable), then smaller blocks propagating faster will simply build a longer chain.