Cryptocurrencies, cardano and crimes

I am going to disagree with most of the posters and say that this is an evolving space.

Blockchains are permanent, immutable ledgers. Over time, the capacity to understand and track activity will continue to grow; regulations will catch up to the technology. There is a permanent record of that transaction if you know where to look - and people are getting much better at looking.

It’s literally impossible to do anything without leaving some breadcrumbs behind. Even something as innocuous as buying an NFT can be enough to track someone; let alone patterns like activity at certain times of day and month.

In terms of reverting - the answer is “Yes, this could be done”. Doing it on the main chain would need something like a widespread vote under Voltaire - so it wouldn’t be done trivially, but if the activity was significant enough, this is something the community will probably be called on to either grant or withhold consent at some point.

Doing things on the main chain has a lot of friction; you need to balance platform risk, the risk of the fundamental rules changing underneath you, with whatever goal you want to accomplish by moving faster. The chain needs to be able to adapt and evolve over time, but not so fast that people can’t be confident using it.

Side-chains open up many more opportunities; they can support wildly different economics and policies than the main chain and by their specialized nature may be easier to tailor a specific solution. Certain activities that require more frequent reversals will require this approach.