According to chainanalysis, about 0.34% of crypto transfers in 2020 were for crime if that's what you mean by illegitimate [1].
1: https://blog.chainalysis.com/reports/2021-crypto-crime-repor...
1: https://blog.chainalysis.com/reports/2021-crypto-crime-repor...
Bitcoin only ever was pseudonymous, which is only anonymous if you manage to disconnect each link between with the real world and your bitcoin pseudonyms/addresses. For ever.
That is a lot of hard work, when for example a £20 bill works so much easier.