Guilt about others serves to sustain the group. The effect of proselytizing is to reaffirm and strengthen a belief system. The psychological term that applies is cognitive dissonance. Humans need to experience internal consistency. You cannot repeatedly say one thing and believe something else without being very uncomfortable, without experiencing dissonance. Therefore, if you are preaching a certain message out of obligation, the easiest thing is to believe what you’re saying. “Witnessing” is a way of convincing yourself on a regular basis.
Additionally if you are busy doing "the work" like you should be then you won't have time for doubts
