The smaller the blocks are, the bigger the fees will be. If hashrate majority will decide to switch not from 1 sat/vB to 0.1 sat/vB, but to 10 sat/vB instead, then that could became de-facto standard. The same, if they would decide to shrink blocks from 4 MB to 1 MB witness, like it was done in Signet.

You think only about short-term profits. Many miners are not like that. To make sure, that their blocks are valid, mining pools often are running full archival nodes, especially if they are handling a lot of coins. And then, the bigger the block size is, the worse for them, because it takes more space, and it gives less fees. So, mining pools have an incentive, to keep blocks small, because then, it is easier to run nodes, and it is more expensive to transact, so they can get more fees out of it.

It is true in many altcoins, and it was true in case of Bitcoin in the past.

Of course he can. And of course a lot of users can contribute to the network's security, if each of them will pay a little. You can pay for security in two ways: one is transaction fees, another is Proof of Work. If you have more coins, then you can pay in satoshis. If you have more mining equipment, then you can pay in Proof of Work, and make even free transactions, as long as you can mine them.

But it can be. It is just a matter of doing yet another soft-fork, similar to Segwit, and increasing the size of the block from 4 MB to 4 GB, 4 TB, or making it unlimited. And then, the decision to reject a future upgrade is in node's hands.

Not that much different than today, because I know, that it is very likely, that the mainchain will be heavily spammed in the future, when next limits will be lifted, one-by-one, and when developers will be responsible for nothing.

Also, regulations like MICA will keep destroying Bitcoin anyway, so it is good to use it, while you can do so legally. But if Bitcoin will be illegal, just like gold was, or if you would need to pass through KYC to use it, then it won't surprise me, because it is already happening.

You won't "be remembered for ages in the chain", because when less and less users will run nodes, and they will be more and more pruned, some nodes may decide to stop serving you historical transactions. There are already much more pruned nodes, than there should be. And there will be only more, and they will be more pruned. If the chain will be still spammed, then future nodes will just store the subset of the mainchain traffic. And then, you will have a choice: wait years to fully synchronize the full chain, by connecting to full, archival nodes, or trust some pruned ones, and accept their proofs, that the chain is valid, without downloading everything.

Because the ability to always fetch any transaction, from any block explorer, is temporary. When BSV became too big, then block explorers stopped handling it. And the same can happen with BTC, if the size of the chain will be bigger, than nodes will be willing to handle.

Because this is how you teleport coins between mainchain and sidechain. If you send one mainchain coin, then you receive one sidechain coin, and your mainchain coins can be moved anywhere. It is the same case, as if you open a Lightning Network channel: if you use one UTXO, and decide to leave the network, then your old UTXO can be handled by someone else, and you can get coins from a completely different channel.

Also, sidechain miners are not working for free. If you use a given sidechain, then you pay mainchain fees, and sidechain fees. It is exactly the same as in LN, where you pay mainchain fees, if you want to join or leave some channel, but you also pay LN fees, when you move coins inside this network.

I thought for a while, that sweeping dust is non-standard. But it seems only sending is, and sweeping can be done normally.

Because it was in your example, as a change address. And I decided to send a small donation.