Thanks for the insightful criticism. I'll try my best to address some the points you make. 1. Alternate Currencies I only have the following to say on this topic, it's not a complete thought so please be gentle:
The value of legal tender is that it is valid for all debts private and public. Alternate currencies have value among the groups that value it. To use this value outside the group, it must be exchanged. This necessarily means gatekeepers and rentiers who exploit their positional privilege to increase their wealth.
*Edit: Also this would be the effect of the Disenfrachisement critique writ large. 2. 'Cashless society' does not equal 'cash prohibition' Maybe a bit sensational but I'm trying to get all this down to elevator pitch length. In fact I do believe that the two are identical. Take the example of JackTheBandit's mother. She has been prohibited from using her hard earned cash to pay for carriage on the M60. Previously she was allowed to, now she is not. The upshot is that her cash is a little bit less valuable now than before. The cashless society will be upon us when, after a progressive series of such prohibitions, cash is deprecated to the point of being valueless.
Also the expression 'cash prohibition' helps to refocus the conversation on the fact that this policy is taking away rights that we previously had. 3. Rent Redux The economic rent that transaction processors already extract is factored into the cost of things that you buy. I doubt their contribution to the effort required to furnish the item to you is worth the x% that they charge. Further, they likely charge a similar x% at every step along the way that was taken to produce and deliver the item. All of these costs must eventually be recouped through the sale price.
The project of cash prohibition is a classic case of rent-seeking as it is an attempt to impose ownership over a resource that didn't previously have an owner for the purpose of exploiting the positional privilege.
Unfortunately this point is a bit obscure but I think it is the second most important one. I would greatly appreciate any help to make it more concise and meaningful.
1. Yeah, I agree. I just think you have to be careful about implying that a cashless society means the absence of any kind of physical currency (rather than just the absence of gov't-backed currency) 2. See 1, and I'm fine with the expression "cash prohibition" as a tool for persuasion as long as you're clear about this being prohibition of gov't-backed physical currency. 3. I'm still not convinced - as you mentioned in the OP, the gov't already charges a sort of "rent" for using currency, i.e. taxes. As such, the shift away from cash wouldn't mean rent where there was none, only a shift in who's collecting the rent. (And re: their contribution not being 'worth it', arguably because there are a number of such providers in competition with each other and the price is what it is, the price is at equilibrium, or close to it, implying that a sizable percentage of consumers do think the rent is worth it.)