Issue in a nutshell:
- On a network where miners do not honor SegWit, all segwit transactions are 'anyone can spend' transactions
- On such a network, each successful miner can spend any 'anyone can spend' transaction to himself
- As segwit is used (e.g., on a segwit-honoring network), more value gets locked up in segwit/'anyone can spend' transactions
- As more value is built up in segwit/'anyone can spend' transactions, this increases the incentive for miners to flip the network from segwit-honoring to non-segwit
- This pressure increases with increasing use of segwit. Even if initially stable, the system tends further toward instability.
The net is that smallblockers need to trust the miners -- whom they seem to already believe to be evil -- to not steal their segwit transactions.
Of course, one can convert a segwit coin back to a bitcoin by spending it to yourself in a non-segwit transaction. But that also mandates a second transaction, thereby nullifying and even reversing segwit's so-called capacity increase.
Sounds very speculative and hypothetical to me.
No. Just No.
Please employ proper logic. Every bulleted item above is a factual statement. Would you like to challenge any of these factual statements on their own merit?
Whether or not those steps get chained together in reality is currently a matter of speculation, yes. But I made no such claim. A set of factual statements is not "speculative and hypothetical". Any speculation as to the consequences of the above has been left to the reader.