The attack quoted from his article:

[Level 2] Anti-split protection — Miners will orphan the blocks of non-compliant miners prior to the first larger block to serve as a reminder to upgrade. Simply due to the possibility of having blocks orphaned, all miners would be motivated to begin signalling for larger blocks once support definitively passes 51{88c91daedd271a990a10650c05d769cae2765e0603edf30ca95f18704e5748e8}. If some miners hold out (e.g., they may not be paying attention regarding the upgrade), then they will begin to pay attention after losing approximately $15,000 of revenue due to an orphaned block.

[Level 3] Anti-split protection — In the scenario where Levels 1 and 2 protection fails to entice all non-compliant miners to upgrade, a small-block minority chain may emerge. To address the risk of coins being spent on this chain (replay risk), majority miners will deploy hash power as needed to ensure the minority chain includes only empty blocks after the forking point. This can easily be accomplished if the majority miners maintain a secret chain of empty blocks — built off their last empty block — publishing only as much of this chain as necessary to orphan any non-empty blocks produced on the minority chain.

If miners can force a hard fork on users, then bitcoin is no longer interesting. The only defense I can think of is a PoW hard fork, miners should not be in control.