A 51% attack on Bitcoin only allows miners to double spend. On a drivechain, they can just steal everything.
It has been said ever and ever, still a very misleading and wrong assertion.
Although I'm not a fan of two-way-pegged off-chain solutions being drivechain/sidechain or something like LN, It doesn't look a good criticism by any means to me. Honestly, I suspect the people who first brought up this argument, could have little if not zero good faith. No offense, I understand you are just re-hashing the same assertion they make in any situation when it comes to discussing anything other than their stupid agenda.
Bad criticism is more concerning and dangerous, sometimes, than the original idea being criticized, as it would have worse consequences than simply accepting the idea blindly, agreed?
Ironically, the same people who proposed and advocated two-way-pegged-sidechains in the first place are the ones who are spreading FUD and fake claims about the idea. Why and how? Let's leave this for the next generation of crypto-historians and journalists and stay focused on this miner-phobic assertion you are rehashing here:
1- Resisting double-spend attack is the single privilege of bitcoin. It is merely a decentralized, trustless solution to the double-spend problem:
Abstract. A purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution. Digital signatures provide part of the solution, but the main benefits are lost if a trusted third party is still required to prevent double-spending. We propose a solution to the double-spending problem using a peer-to-peer network. The network timestamps transactions by hashing them into an ongoing chain of hash-based proof-of-work, forming a record that cannot be changed without redoing the proof-of-work.
Period.
2- At the time of this writing and for the foreseeable future there is no double-spend threat to bitcoin, and it is why in its worst days, bitcoin holds a whopping 100 billion dollars market cap.
3-I'm well known for my strong opposition to the current situation with pools and ASIC manufacturers, but it doesn't imply that I think there is any chance of double-spending in bitcoin, otherwise I wouldn't waste a minute counting on bitcoin and would have been criticizing it as a failed project.
4- A hypothetical collusion by miners against a sidechain in the future, will make my above argument void as it proves the mere existence of a 51% that exposes bitcoin to double-spend and censorship threats. This would be apocalyptic and thanks god, it is not considered feasible as far as the market and the community are concerned.
5- Suggesting such hypothetical miner-collusions as "a security hole" or "something concerning" for sidechains is absurd too as it is applicable to every single two-way-pegged solution, the most distinguished one being LN. e.g. they could selectively censor/nullify anti-cheat punishment transactions in favor of their own fraudulent behaviors in the network and our superhero full nodes would have absolutely no clue about the existence of the problem, forget about being helpful.
I suppose such criticism is political rather than game-theoretical/technical, hence strongly recommend not to follow this trend, no matter who is
backing it.
On the other hand, this is meaningless to suggest any kind of proof in such systems, other than (SPV like proof of) work. Securing the "reclaiming phase" in sidechains by relying on or even having involved full nodes, would existentially nullify the off-chain idea, either it is the traditional verification or zk alternatives.
Zero-knowledge proof is decent technology, but once it becomes practical, it could be employed on the mainnet as well, causing a radical shift of concerns.
