Leaving aside the legality for the moment, because it's complex, jurisdiction-dependent, and constantly in flux, "crypto transaction laundering" is not in and of itself unethical. It depends on what you are intending to conceal. The parallels to encrypted messaging are really quite strong IMO.

If you are trying to hide a purchase (with your own money) from your wife because you think she wouldn't approve, that's totally ethical (if a bit of a silly relationship tactic). Similar if you're trying to hide a donation to an unpopular politician or charity from your employer. If you're trying to hide a donation to a militant organization, it's much more ethically complex and depends on the goals and actions of the organization. If you're trying to hide the source of ill-gotten money, it's likely unethical.

Separately, while the tool might be "primarily" used for unethical things, that does not make the tool unethical itself. Again it is the actions of the users that determine this. Even if hypothetically 95% of Tor users are pedophiles and ransomware crackers, that does not invalidate the "legitimate" ethical use of the tool by the remaining 5%.