Spending old coins doesn't violate the rules of Bitcoin. Who said otherwise? The rules can be changed though, by any set of users. While a controversial change probably costs more than it benefits the group going along with it, if a supermajority wants the protocol to go in a certain direction, sure, the tiny minority can fork off, but they probably won't be able to maintain such a minority fork. So if we all assume (we can't know exact figures) that 20% of bitcoins are essentially unrecoverable by their original owners but could at some future point be recovered through brute force due to their public key crypto becoming weak, then as Bitcoiners we have to decide whether to allow this or not. There are engineering and political risks, but in the end users will decide one way or another. I'm for "freezing coins" that could otherwise be brute forced, and for providing alternative recovery paths where weakness-proof mathematical proofs are possible. That said, I probably wouldn't sell all my coins on a super-majority non-freezing fork to the other side. I'd shout "you fools" at the void and accept that billions of dollars will get wasted on quantum mining of old bitcoin wallets, while hoping there would be some other useful stuff that could be done later with all the quantum mining equipment so it doesn't end up as QC's only use case.