Absolutely not! Unless they become physically violent, or engage in abusive or harassing behavior that threatens you or your comrades' personal safety, there is nothing to be gained from being a snitch against other leftists. Yes, even very hostile and misguided ones.

Lenin had serious disagreements and even personal enmities with plenty of people and parties that claimed to be Marxist but were really leading people astray, and he engaged in ruthless ideological struggle against them, but he never denounced them to the Tsarist police.

That is the quickest way to become reviled among the people you are trying to appeal to.