Ethically, this situation has some similarities to the DAO fork. We have an entity who closely examined the code, found an unintended characteristic of that code, and made use of that characteristic in order to gain tens of millions of dollars. Now that developers are aware of it, they want to modify the code in order to negate as much of the gains as possible.

There are differences, too, of course: the DAO attacker was explicitly malicious and stole Ether from others, whereas Bitmain is just optimizing their hardware better than anyone else and better than some of us think they should be allowed to.

In both cases, developers are proposing that the developers and a majority of users collude to reduce the wealth of a single entity by altering the blockchain rules.

In the case of the DAO fork, users were stealing back stolen funds, but that justification doesn't apply in this case. On the other hand, in this case we're talking about causing someone a loss by reducing the value of hardware investments rather than forcibly taking back their coins, which is less direct and maybe more justifiable.

While I don't like patented mining algorithms, I also don't like the idea of playing Calvin Ball on the blockchain. Rule changes should not be employed as a means of disempowering and empoverishing particular entities without very good reason. Whether patenting a mining optimization qualifies as good reason is questionable.