Right now ethash network is fully protected, nobody can have 51% total hashrate, with asics that can be true, right now eth hashrate is totally decentralized, btc hashrate is mostly centralized and that is bad.
ETH also has a very functional and active dev team. If eth ASIC's should materialize, they might just do a fork to change the algorithm a bit, it would be in the interest of the network. Then bitmain will be stuck with a pile of useless hardware that took millions to develop and manufacture, that kind of lesson would serve as the best ASIC deterrent.
A lot of people thought the same with sia. That did not happen. Its good to keep things decentralized and open market. There will be a use for these ASICS regardless of Eth ever goes pos. Which btw hasnt happened for last cpl years but has been a threat for many reasons as I have witnessed. We should let it play out and see where it goes.