Prayer: Can one pray behind an Imam they doubt, just for unity?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: Can one pray behind an Imam they doubt, just for unity?

English:

Question #614:

If a mukallaf does not consider the appointed Imam of Friday prayer as just or has doubts about his justice, then are they allowed to perform their prayers behind him just to maintain the unity of the Muslims? Furthermore, can a person who does not attend the Friday prayer discourage others from attending it?

Answer #614:

It is not correct for a person to perform prayer behind one who is not considered as ‘ādil or about whom the follower doubts his justice. Nor would his congregational prayer be considered correct. However, for the sake of unity, there is no problem in joining the congregational prayer. But this person is not allowed, under any circumstances, to encourage others not to join the Friday prayer.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer