Yeah, taking Momentum as a UK example, they certainly seem to have got their act together as a machine for using social media for targeting and recruiting the young voters. However, that’s probably the most leftist of the influential political groups out there and the policies they’re putting out are not even close to hard left. We had nationalised rail and utilities when I was a kid, but even the Tory government in the 80s never described that as communism!
Also, whichever way you lean politically, the messaging is different; advocating increased spending is risky from a taxation point of view, but ultimately the message is one of improvement and is not an outright lie, though many disagree with this ideology you don’t see many examples of outright lying. The messaging that the problems in the UK can be solved by things like curbing immigration (which ties nicely in with the Brexit fiasco) are simply factually inaccurate, or, what we used to call lies.