In modern English "do" is obligatory for forming negations and questions, unless there is an auxiliary verb (or the substantive verb is "be", or for some speakers "have").
A passive is formed with the auxiliary "be", so it is not negated with "do":
"A, B and C are compared"
"How are A, B and C compared?" (Not "How do A, B and C be compared?")
If another auxiliary, such as "can" is used, the same thing happens, whether or not there is also a passive auxiliary:
"A, B and C can be compared"
"How can A, B and C be compared?" (not "How does A, B and C can be compared?")
On the other hand, it is common in speech to express passive meaning by the word "get", as in
"A, B and C get compared"
but "get" does not behave like an auxiliary, and does require "do":
"Do A, B and C get compared?" (not "Get A, B and C compared?").