No. Darknet markets also sell things that are unambiguously legal to buy everywhere, as well as products that are legal in some countries but not others. The products on sale are far from only the stereotypical drugs porn warez and fraud (and no you cannot buy assassination on darknet markets; any such offers are a mix of law enforcement stings and scams which take place without any marketplace providing escrow).
If nowhere but darknet markets let you buy a car with Bitcoin or Monero, then only darknet markets are what someone who has cryptocurrency and wants to buy a car with it will use. That being said, you can exchange cryptocurrency for a car safely and legally, without touching a DNM or doing anything shady.
If nowhere but darknet markets let you buy a car with Bitcoin or Monero, then only darknet markets are what someone who has cryptocurrency and wants to buy a car with it will use. That being said, you can exchange cryptocurrency for a car safely and legally, without touching a DNM or doing anything shady.