This is true, but miners already control block size through soft caps. Miners are fully capable of producing smaller blocks regardless of the max block limit, with or without collusion. Arguably, there is no need to ever reduce the max block size unless technology advances for some reason reverse course - aka, WW3 takes a toll on the internet and the average bandwidth available halves. The likelihood of significant technology contraction in the near future seems rather unlikely and is more broadly problematic for society than bitcoin specifically.

The only reason for reducing the max block limit other than technology availability is if you think that this is what will produce the fee market, which is back to an economic discussion - not a technology scaling discussion.

On Tue, Sep 8, 2015 at 4:49 AM, Btc Drak via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

> but allow meaningful relief to transaction volume pressure in response to true market demand

If blocksize can only increase then it's like a market that only goes
up which is unrealistic. Transaction will volume ebb and flow
significantly. Some people have been looking at transaction volume
charts over time and all they can see is an exponential curve which
they think will go on forever, yet nothing goes up forever and it will
go through significant trend cycles (like everything does). If you
dont want to hurt the fee market, the blocksize has to be elastic and
allow contraction as well as expansion.