Entryism is different, entryism is when you try to seize levers of power from within institutions that already wield power. Bernie Sanders was arguably doing entryism with the whole idea of a "political revolution" but the liberal establishment is too adept at blunting and coopting any left populism within its own ranks. OP is talking about people joining organizations to sabotage their efforts to work outside those power structures.
it sounds like you mean entryism
Entryism is different, entryism is when you try to seize levers of power from within institutions that already wield power. Bernie Sanders was arguably doing entryism with the whole idea of a "political revolution" but the liberal establishment is too adept at blunting and coopting any left populism within its own ranks. OP is talking about people joining organizations to sabotage their efforts to work outside those power structures.