There is obviously going to be a market even if there is no scarcity with the block size. It's not going to be much of a market, the fees would go really low and the hash power really low as well, but there would be a "lowest point" so to speak.
Let me make sure I correctly understand what you're saying.
If miners are not limited by protocol to a fixed block size, space in the blocks will no longer be scarce. Miners have an infinite amount of bandwidth, disk space, and processing power so they will be able to include an infinite number of transactions in a block with absolutely no marginal cost, because if any of these things are not true then space would be scarce.
Because miners have the infinite capability to generate blocks of unlimited size, they will automatically do so. This will make space in the blockchain is free nobody will include fees in their transactions. The
only possible option miners will have to respond to this by quitting mining entirely, strangely even though we already established they have infinite free bandwidth and processing power to mine with.
Bitcoin will fail because mining, like every other business in the world, becomes cripplingly unprofitable if the industry is allowed to increase capacity to match higher demand. The amount of transactions that can be processed
must remain fixed in order for people to be willing to invest capital equipment into mining and thus keep the network secure. It's just like how we limit the worldwide car market to 100 new cars per year in order no matter how many people want to buy. It's the best way to keep the industry decentralized.