A:

• You should respect C's belief, for all beliefs are of equal validity and cannot be denied.

B :

• I deny that belief of yours and believe it to be invalid.
• According to your statement, this belief of mine (1) is valid, like all other beliefs.
• However, your statement also contradicts and invalidates mine, being the exact opposite of it.
• The conclusions of 2 and 3 are incompatible and contradictory, so your statement is logically absurd.