I'm pretty much the opposite of a bitcoin fan, but I think if you replaced "bitcoin" with "dollars" in your comment you would see that it sounds a bit weird. I bet most dollars have been involved in shady business at some point during their life. With bitcoin you have a better chance at figuring this fact out I guess.

Regarding quantum computers: Quantum computers are not known to be exponentially faster at hashing than normal computers, so they pose no threat to bitcoin.

That is true.

On the other hand, while I'm (unfortunately for this discussion) not an expert in money laundering laws, the police tend to confiscate money that is known to have been laundered (or even before they know for sure apparently). Since Bitcoins are trackable, tumbled bitcoins should be "confiscated" (by marking them as illegal for use in @countries in some kind of database) and then, if the previous owner proves that they weren't doing anything illegal, unmarked. Once there is proof of illegal activity, the previous owner could be forced to return them to the rightful owner (if a rightful owner exists, such as in the case of ransomware), or either kept marked as confiscated or even marked as permanently invalid.

Best of luck enforcing that. Just like cash, most people are not going to care if someone pays them with laundered BTC, and will ignore the law. Even if they do manage to get enforcement in place years down the road, that kind of activity will not happen with BTC. People who value privacy in their transactions already use Monero, which is superior to BTC in that respect

Quantum issue is not with hashing but with private key derivation

Oh I didn't know that! Thanks for pointing it out.

But quantum computer can break currently used Public-Key Algorithms, like ECDSA, which is used by Bitcoin.

>- How about people stop accepting laundered bitcoins first and foremost?

How do people know its laundered? If they know, its likely they're complicit so unlikely to stop if being asked to...

> - Any bitcoins that have provably been involved in illegal stuff

See above

> - Any monero/whathaveyou that come from exchanges that accept bitcoin that have received Bitcoins that were involved in illegal stuff

See above also

>- Will bitcoin still have value when quantum computers are around?

Why not? Its reasonable to assume that any increasing capability in hardware will likely also benefit design and capability of software. They'll just make the maths a lot lot harder (to be absurdly simplistic)

Easy in the case of ransomware or any other cases where a victim has to pay Bitcoins. The entity who pays the ransom/whatever sends the money to a Bitcoin address. This money is immediately marked as "confiscated" in cooperating jurisdictions. That money will be mixed in a tumbler (operating in a non-cooperating jurisdiction) with other Bitcoins, which get the same treatment. Or exchanged for a different cryptocurrency in an exchange that facilitates money laundering, and all cryptocurrency that is traceable that goes through that exchange is immediately marked as "confiscated".

You can keep using Bitcoins in non-cooperating jurisdictions, sure. But they'll automatically be less valuable or worthless because you can't use them in many countries.

People with development experience in Bitcoin could implement this in a jiffy. Doesn't even take a government really, you could probably build a startup whose main thing is to provide this information. Then people/exchanges/etc. could decide on their own if these Bitcoins have value or not.

Yes. Vitalik Buterin (Ethereum founder) talks about this in his talk with Lex Fridman. According to him, the overhead of running a Quantum computer will be higher than the speed-up advantage you get by using it for mining.

Link to his talk https://youtu.be/3x1b_S6Qp2Q?t=2580 (43:00)