Andre, your rationale is broken.
Let's say tomorrow morning block size is 10mb.
I spam it to "full blocks". After all, fees are dirt cheap (even now, 42k txs were processed in the last 24hrs for near zero fees at the 0 to 9 satoshi range -
https://bitcoinfees.21.co ) since there's around 0.7-0.8mb actual demand (or at least pretending to be actual by paying 10+ satoshi) and no practical fee competition for the rest 9.3mb.
So once I do that, I come and tell you that there is no room for new users because txs are maxed out.
Spot the fallacy.
No, it's your rationale that is broken. Because you assume that low paying txs are spam. But if they are spam, why pay anything? It's like saying the passenger who bough a $10 plane ticket isn't really going anywhere -- he's just spamming the airplane, because his ticket is so cheap (look! 42 of the 250 passengers had a $10 ticket on the last flight!). I disagree with your assumption. I think cheap customers are still real users of the airline. And by selling their seats to others who pay more, you are not flying more passengers. You are not increasing the user base.
You may disagree all you want but the reality of economics is that if you give the service for free or near-zero, it will attract abuse. And you can label that abuse as "use", to make the case for 10mb or 10GB blocks - which even them can be filled by abuse, and then you will be asking for 10 PB blocks: You implement circular logic, using the maxed transactions as evidence for "we can't have new users", forgetting that one can max out
any tx limit if the cost for doing so tends to zero.
Your logic is also provably problematic, because altcoins have actually tried adaptive block sizes where the block just grows with use - and guess what happened.... Abuse happened. It started growing and growing in tx count, and then the blockchain was getting more bloated and more bloated, and guess what was the reaction... Minimum fee was raised. A LOT. So, in the end, while block size was "infinite" to cover any demand, in reality it was just only serving top-paying customers to keep bloat to a minimum and prevent spamming.
If the block has ample size for txs and if fee tends to zero, abuse will tend to max block size - just because some random hacker or script-kiddie wants to do that. You either implement a minimum fee threshold and larger sizes, or you let a block size that is ok for the market demands and allow a level of abuse with free/near-zero fees (like we have right now).