> a
rhetorical trick as old as time
It is actually a means of pivoting to a different subject, and the next step is to make the subject the person doing the pivoting, and from there to change the entire scope of the discussion to the interpersonal dynamics of the parties involved in the discussion.
On the left (whom I would count myself among, even if I would hardly pass a purity test) there are many ways to do this, the key to all of them being that there's not a serious attempt to engage with the substance of the matter but simply to use an intersecting contextual facet as a means to collect the focus away from the topic and toward the discussant. Racism is probably the most straightforward path, or at least the most well-traveled (of the two mentioned in this thread, it would outrank abortion by being more generally applicable across age groups sexes religions etc) it goes "this isn't about x, x is really about racism. Your position on x implies you might be a racist. That position is personally offensive to me, who is directly or indirectly affected by racism." Done. conversation is now about people, and specifically two individual people, and specifically about the unfalsifiable statements about the feelings of one or both, and this is where it ends.
The right wing version of this trick, at least in the US, is much clumsier and ham-fisted but follows from the same motivation to replace the confrontation with an idea with a personal confrontation, though unlike the progressives they have only managed to devise one or two lasting variations of this same discussion-jamming measure: the pedophilia track and the socialist / communist sympathizer track.
I'm at a loss as to how to even attempt to have conversations in public about anything that matters due to the ever-present danger of one of these tactics surfacing and rendering the entire effort pointless. Perhaps we need to revive IRL coffee shop culture of small close circle debate from the 1800s, or import something like it from wherever a form of it still exists, maybe morocco or turkey.