Attackers could reach 1% of the hashrate, and then they can put a lot of inscriptions for free every 100 blocks.
There's no such thing as free block capacity. The actual cost of these inscriptions would be the high-paying unconfirmed transactions that could be included instead.
when you can store the source code on some place like the blockchain where a third party doesn't have the ability to remove your account.
Source code is frequently updated. You can't go and upload a new source code for every single commit. That's why we have git.
i would say a properly designed payment network would only store utxos anyway.
You can't make sure they are real UTXO if you don't start verifying everything from block 0. So you don't have a "properly designed payment network" if there are no full archival nodes.