As far as criminal activities are concerned countries percieve the impact of crypto to be rather significant. So even if 1% of crypto transactions are related to criminal activities, but 40% of all relevant criminal activities are handled in crypto, it is still a problem. I will not take a stand on wether banning crypto is effective in alleviating that or not, but it can certanly score some political points to be tough on crime and therefore be tough on crypto as well. So yeah, some calculations in banning crypto are related to criminal activities. Though it is certanly not the sole or even the most important consideration
Did you think there's no criminal or money laundering using fiat money? lol, Bitcoin exist since 2008, while criminal or money laundering already exist so long time ago, of course they're using fiat money to do that. You should look at this article
https://www.linkedin.com/pulse/comparing-money-laundering-cryptocurrencies-fiat-aly-madhavji-%E7%A9%86%E4%BA%9A%E9%9C%96Where the money laundering using Bitcoin is completely far than using fiat money. Criminal can use Bitcoin as an option, but you need to spesk with the data and fact about how much the Bitcoin usage by criminal rather than talking like you're know anything.