I have some understanding of "parametric" vs "mesh". I looked it up when I saw so many people going on about it.

Maybe it is the export or something. I run the 3D toolbox and often models are not manifold.

I see things like two circles in slightly different positions but both are connected in different ways to the surrounding "single" instance model. Things like this mean you end up with "infinitely small volumes". There is no fully enclosed "volume" and so mathematically there is "nothing to 3D print".

As a model this makes no sense to do, and so it irks me.

But clearly the slicer software doesn't care or autocorrects and people make their 3D print happen just fine.