If non-gmo produce tastes so much better then people will buy it and farmers will still grow it, but cheaply available produce is a clear win for everyone. And as I said in the other comment, you can have GMO without monocultures if the need arises.

The fear of eating it is all baseless fearmongering by the likes of homeopaths and crystal healers.

I largely agree. On specific crops this is a particularly worrying concern—see eg foreign crops. These are largely monoculture and are particularly vulnerable to eg disease. However, I see this as a lost battle.

They'll learn the lesson to introduce more variance after the first big incident, if it happens.

What makes you think the industry will survive the first?