Thanks @quintuskilbourn! This touches the core of the issue, so it leads me to clarify and re-explain some points and also add a few things.
In general terms, I consider your statement correct and this is why I’ve left open the possibility of a trade fee. This means a fee –beyond the gas fee– that is increasing (possibly sublinearly) in the traded amount. See the first of the “final remarks”. The way I would implement this according to what I think today, is to allow trade orders to specify freely the maximum gas+trade fee. There are however good reasons to believe that the market will permit low trade fees. Moreover, I wouldn’t rule out zero trade fee as a common practice. Notice that each of the following two facts contradicts your first statement, strictly speaking. Allow me to repeat myself here and there.
-Since the mechanism clusters together the most liquid tokens, once you mess with the price of one token you break the equilibrium of the whole cluster. Thus you may miss not only censored trade orders but also trade orders corresponding to different pairs that fell off because you moved the price.
-The presence of honest solvers will enable users to send their orders exclusively to them. As a result, dishonest solvers will be at a significant disadvantage, as they will miss out on a crucial portion of the order flow.
The role of honest solvers would likely converge with that of block builders. This role is inherently oligopolistic: since the total revenue will only represent a marginal portion of the block’s value due to the proposer’s monopoly, a large number of honest solvers would be unsustainable. The permissionless feature gives fluidity to the system, allowing the replacement of the members of this oligopoly.
A nice feature of this picture is that it naturally defines what is a honest solving algorithm. If it converges with block building, it would be way more transparent than current status quo where it is even unclear which behaviors are ethically acceptable, and the algorithms used by top block builders are hidden.