This is a double-edged sword that almost everyone points out the bad side of. The good side is that because GPU miner’s hardware is less specialized (they can always sell the hardware at a loss or mine another coin), they will not dig as deep a position against an existential threat to their operations (for example, the upcoming move to PoS and the mining reward reduction when we employ the finality gadget). If PoW mining were the long-term goal of Ethereum, then it would absolutely make the most sense to adopt an ASIC friendly position, because that type of deep hardware investment aligns these actors long-term with the health and security of the current chain. But we are not trying to do this! As a community we are looking to make a move to a completely different consensus mechanism that eliminates the need for any sort of mining over time.
To respond to the specific criticism though, rental attacks hold true for any PoW algorithm, no matter what is considered the most profitable hardware for mining it (CPUs, GPUs, ASICs, etc.). In the general case, if you do not have a supermajority share of the hardware considered to be the most profitable for mining a particular PoW algorithm, you will be at risk to a rental attack. Ethereum currently attracts the largest share of GPUs used for mining. If it were to change it’s algorithm to something that attracts more specialized hardware, that currently mines another coin more profitably, the network would become much more insecure as a result. Therefore changing to another algorithm where the GPU is not the most profitable hardware for mining it would almost certainly lead to a loss of security over what we currently have. It also represents a centralization of power as these manufacturers are much better coordinated and have larger incentives to disrupt any unprofitable changes than to current mining algorithm. It simply should not be done.
I don’t think it’s controversial to say we should either make a change in an attempt to further ensure ETH is the most valuable coin for GPU miners to mine, or accept that we as a community no longer value ASIC resistance and we prefer to let specialized hardware own our network security from the near future onwards, for better or worse. The later option will happen by default as it does not require any change to the current technical design of Ethereum, but we should recognize it represents a change to the social contract laid out from the beginning in the Whitepaper. However, deciding to go all in on allowing ASICs may see an exodus of GPU miners as they divest themselves from involvement in our community, so we may see short term insecurity as a result. Failure to make an active decision one way or another represents a win for specialized hardware manufacturers, and invites them to make further investment into our ecosystem with the knowledge that they can win against the community on any dispute much easier than if we did make an active decision.
Whatever we decide, it should be understood that it may come at the detriment of our future plans for a transition to PoS.