I can't speak for the people buying into this crap, but if you look where it originates from it's very often tied to people, organizations or states that simply want to destabilize the countries and populations it's aimed at. Hence the 'throw everthing and see what sticks'. There's no real need for any of it to come true in the long run, and often no real interest in the actual content of the issue; it's all about destabilizing, undermining unity, etc.
In Russian eyes, long term stategic health problems and societal divide as a result of all this antivaxbullshit is a complete win simply because it weakens western societies by destabilizing them. Similarly they'll latch on to anything else that can create or amplify fissures, be it a farmers protest, racial issues, focus on ethnonationalism, leaving the EU (Brexit was arguably the biggest succes Russian secret services had within Europe), etc. Similarly, in the past Russia has also been tied to amplifying and/or supporting certain green movements because their interests alligned. So for example they were pretty big on supporting anti-shale movements in Eastern Europe because it would have led to energy independence from Russia if they went down this path, taking away their main source of leverage.
Once you know what to look for it becomes pretty straightforward to recognize the Russian trolls, Russian bought-and-paid-for 'politicians', or people who bought into or read their message. There's a lot of common strands.