But isn't it so that, with sufficient sized samples, the 'chosen' as opposed to random mating becomes statistically or actuarily irrelevant - depending on
what you are studying?

"Depending on what you are studying" is a good point here. In some cases it is relevant, in others it is not. In which cases it is relevant? We mostly don't know.

The whole point, I thought, of modelling was to come up with a coarse grain insight into what is happening to the system. There is some limit of fine grainness' in all models: like the limits we use all the time - for instance we see people as entities, as not bunches of atoms. It helps in navigation.

The point is not a reductionist argument. I think it is, if anything, more of the opposite.
Most of these models present themselves as a "precise and rigorous" approach when you cannot have that: Rigorous computations are made on top of massive unknowns and presented as almost hard science because the method is precise, but based on, at best, speculative assumptions.

Taking your example, it is if wrong and/or unknown models of atoms were used in order to make simulations to talk about sociology. It is reductionism based on bad models and precise computation devices in order to give any conclusions the authority of mathematics.

Or taking your photo example it is as if having an originally very bad photo one tried to used the best methods in order to enhance well beyond the information you have there.

Your photo metaphor has actually a severe problem: when you look at a photo, you can easily observe if it is appropriate to your needs or not, when you look at some of the data, theory and models you really don't know if it is appropriate for your needs, as the problem is way complex.

I would be much more comfortable with rougher modules and rougher methods. But of course, that would make things less authoritative and conclusive and would diminish the importance of people doing theoretical work.

Theoretical work that is, sometimes used to make important decisions in things like deciding drug deployment policies or how to intervene in saving endangered species.

Of all forms of caution, caution in love is perhaps the most fatal to true happiness - Bertrand Russell