Non-conductive masts

I read at Hamuniverse that under no circumstance should one use a non-conductive material as an antenna mast. But why not as long as the antenna and coax are correctly grounded using proper materials like deep sunk copper coated rods all connected together by copper strap? Non-conductive materials like pvc are lite, strong and easy to take up and down especially on a tilting mast. Of course all the ham equipment in the shack would be all grounded to a common plate with copper strap into ground rods. The antenna would also have a lightening arrestor likewise grounded into the common ground.
What is the problem with that set up?

nothing … and you should go with it

You’ll find the white Schedule 40 PVC will flex somewhat in longer lengths, requiring that any tall use will require substantial guying.