25mm tyres

20mm tyres.

Less contact with road = less chance of hitting something sharp.

Imagine walking across a room of broken glass barefoot vs tiptoe. If you're lucky, barefoot you might not get any splinters. If you're unlucky, tiptoes, and you hit a piece of glass you can guarantee you'll get a splinter! Same deal, the higher pressure your tyre runs, the greater your chance of punctures.

(as for aerodynamics. I read that 23mm tyres give optimal aero dynamics, as they offer the best balance of cutting through the air and pushing the air away from the wheels.)

The pushing/cutting analogy is misleading. The optimal tradeoff with 23mm tyres is simply between weight, rolling resistance, and aerodynamics, for typical racing use.