We don’t let them; they sneak in. They whip off the masks when they think they are powerful enough and entrenched enough.
In Ireland’s case, the leftism was there since the beginning of the twentieth century. Most of the Easter Rising leaders were communists, the most prominent example being James Connolly; even Lenin (a fellow Second International member) was inspired by Connolly’s efforts.
And of course, the IRA has been proclaiming their “one struggle” with the “Palestinians” for decades . . .
“And of course, the IRA has been proclaiming their “one struggle” with the “Palestinians” for decades . . .”
I believe the same British politician decided the fates of those two peoples in 1917 (hence the “one struggle”); culturally and historically nothing else connects them.