> It breaks easily

Somehow I've never had plastic parts break in the two decades I've been using computers and I don't think I'm in the minority.

> it doesn’t support the non-plastic pieces (e.g. the monitor)

Support how? Are you physically putting your monitor on top your laptop?

Not the person you're replying to, but I have had part of the hinge break in an HP laptop.

Unlike aluminium, plastic doesn't give you electric shocks if you're plugged into a poorly grounded socket: https://apple.stackexchange.com/questions/32417/how-can-i-av...

The link describes them as "minor shocks" but I once had a severe enough shock that I needed medical care.

I guess the point is "citation needed". What you said is "common sense", but the source of that "common sense" is mostly marketing material. At least I don't recollect seeing any hard data, that would support either of those claims.