Believing that it doesn't have an NSA backdoor is reasonable. However, you can't throw it around the board as a fact. We don't have evidence of it being free of backdoor. We simply know that it's open for public scrutiny years now, and that a backdoor in such an examined algorithm would be likely discovered by now. That doesn't nullify the doubt.

Cash has existed for centuries, in much larger scale, and is less traceable than Monero. Yet, no user was subjected to using its banknotes for "mixing". Everyone accepted it.