I have the type of weed whacker that takes about a foot long plastic
"string".

I buy the weed whacker string in bulk, so it's cheap but it only lasts a
few minutes in touch terrain.

I wonder. Would it work to just put an electrical wire, maybe 14 gauge or
so, into the weed whacker?

I mean, why does it use plastic? Why not copper or steel wire (from a coat
hanger perhaps)?

Is it that it would be too dangerous? (But plenty of things are dangerous.)