No one is going to (convincingly) argue that including a monkey jpeg in a transaction is _unlawful_ and so for commercial miners there is always going to be a price where they will include them-- and that price is lower once excessive filtering pays for the creation of submission mechanisms (as it already has done).

But when the censorship is backed by threat (even if vague or unconstitutional) of civil or criminal legal penalties, the avenue to just bypass may be much less available.

So for example, in an alternative universe: Bitcoin goes along with Guida and after having built this massive edifice of transaction censorship the Bitcoin developers lose their UK lawsuit Craig S Wright after he successfully bribes a judge, and now have a the UK courts imposing a worldwide order to freeze any of their bitcoin address under threat of imprisonment.  The censorship is deployed via the prebuilt censorship infrastructure, and willingness to bypass it is greatly decreased because doing so would land the bypasser a UK arrest warrant. Could they still get their transactions through?  Probably but at much greater costs and delays, creating a significant harm.  Not building the censorship infrastructure (even though you intend it for 'good' purposes) and instead building anti-censorship infrastructure leaves us all with a better world.

A world that, sure, sometimes has higher transaction fees due to waves of well funded spam--- but that's just the cost of having limited capacity on the network to preserve the ability to validate and to provide income for security.  It's not a cost of spam itself:  Even if there was never any spam at all there would sometimes be elevated transaction fees due to surges in demand.  Essentially the energy behind this anti-spam stuff is just relitigating the blocksize war, but doing it under the cover(?) of undermining a foundational property of Bitcoin: that bitcoin was created to escape other people passing judgement over which existing transactions are okay or not.  The Bitcoin project has never seen that to be its role.

Prior to Bitcoin your ability to transact "could always be overridden by the admin based on his judgment call weighing the principle [...] against other concerns, or at the behest of his superiors."  If someone cares that someone else is using bitcoin for things they don't like, or that being outbid can delay their transactions-- then they ought to be using something else.  This was settled long ago.

That's the problem with all this filtering stuff:  It works better, to the extent it works at all, against sincere usage which lacks the flexibility of spam (or outright attacks).  Sincere usage cares that the network validates its rules, it has to spend specific coins, specific values, use specific fields.   Collateral usage (a term that I think better captures most of what people are calling spam)-- where the goal of the transaction isn't really to move Bitcoins-- can do virtually *anything* with its transactions, it is far more flexible and so it is less vulnerable to attempts to filter it.