Granted. You have somebody crawling through your vents now.

Are these crawlable vents still realistically filled with dust, dead bugs, mouse droppings, etc?

Are they also now also structurally sturdy and secured enough to support a full grown human being, and not just, you know, air?

Granted, all vents are now the size that they appear to be on a 29" tv

Granted. All humans now shrink to an average size that fits in the smallest air vents.