Drivechain is, in essence, just a way to give Bitcoin users the option to deposit their coins in a hashrate escrow. If Bitcoin is about coin ownership, in theory there should be no objection from anyone on users having the option to do that: my keys, my coins etc. In other words: even if you think hashrate escrows are a terrible idea and miners will steal all coins from that, you shouldn't care about what other people do with their own money.
There are only two reasonable objections that could be raised by normal Bitcoin users against Drivechain:
- Drivechain adds code complexity to
bitcoind - Drivechain perverts miner incentives of the Bitcoin chain
If these two objections can be reasonably answered there remains no reason for not activating the Drivechain soft-fork.
1
To address 1 we can just take a look at the code once it's done (which I haven't) but from my understanding the extra validation steps needed for ensuring hashrate escrows work are very minimal and self-contained, they shouldn't affect anything else and the risks of introducing some catastrophic bug are roughly zero (or the same as the risks of any of the dozens of refactors that happen every week on Bitcoin Core).
For the BMM/BIP-301 part, again the surface is very small, but we arguably do not need that at all, since anyprevout (once that is merged) enables blind merge-mining in way that is probably better than BIP-301, and that soft-fork is also very simple, plus already loved and accepted by most of the Bitcoin community, implemented and reviewed on Bitcoin Inquisition and is live on the official Bitcoin Core signet.
2
To address 2 we must only point that BMM ensures that Bitcoin miners don't have to do any extra work to earn basically all the fees that would come from the sidechain, as competition for mining sidechain blocks would bid the fee paid to Bitcoin miners up to the maximum economical amount. It is irrelevant if there is MEV on the sidechain or not, everything that reaches the Bitcoin chain does that in form of fees paid in a single high-fee transaction paid to any Bitcoin miner, regardless of them knowing about the sidechain or not. Therefore, there are no centralization pressure or pervert mining incentives that can affect Bitcoin land.
Sometimes it's argued that Drivechain may facilitate the ocurrence of a transaction paying a fee so high it would create incentives for reorging the Bitcoin chain. There is no reason to believe Drivechain would make this more likely than an actual attack than anyone can already do today or, as has happened, some rich person typing numbers wrong on his wallet. In fact, if a drivechain is consistently paying high fees on its BMM transactions that is an incentive for Bitcoin miners to keep mining those transactions one after the other and not harm the users of sidechain by reorging Bitcoin.
Moreover, there are many factors that exist today that can be seen as centralization vectors for Bitcoin mining: arguably one of them is non-blind merge mining, of which we have a (very convoluted) example on the Stacks shitcoin, and introducing the possibility of blind merge-mining on Bitcoin would basically remove any reasonable argument for having such schemes, therefore reducing the centralizing factor of them.