I am looking for a saying or idiomatic expression about a person from a community who attacks (verbally) his own members just to please the members of the other community on an controversial issue. The two communities can be at peace but in the past there were some tensions that surface at some times. The attacker can have a point on a controversial issue but that is difficult to gauge. In this context, the attacker crosses the red line from just critique to (mostly) offense. It is just to say that the attacker can only please the members from the another community who already are somewhat hostile to the first community members; not all members from another community appreciate this attack on his own members.
In Latvian there is a saying that literally translated says: "[because of what he said] he will be beaten by both sides." Beaten by both sides implies that he annoys the members of his community and also by other community because he does not really belong there or get accepted there. Beaten here does not mean physical beating.