This phrase is nonsense, because HFCS is a chemical process applied to normal corn after the harvest. The corn may be a GMO but it certainly doesn't have to be.
While their nutritional quality has gone down tremendously, for vegetables too: https://pmc.ncbi.nlm.nih.gov/articles/PMC10969708/
Here is a list of approved bioengineered foods in the US:
https://www.ams.usda.gov/rules-regulations/be/bioengineered-...
All the fruits on the list are engineered for properties other than sweetness.
The term you're looking for is "bred". Fruits have been bred to be sweeter, and this has been going on a long time. Corn is bred for high protein or high sugar, but the sweet corn is not what's used for HFCS.
Personally, I think the recent evidence shows that the problem is not so much that fruit is too sweet, but that everything is made to be addictive. Satiety signals are lost or distorted, and we are left with diseases of excess consumption.
But I constantly battle tested them against other smart people’s views, and just after I ran out of people to bring me new rational objections did I become sure.
On a lesser level of confidence, I have also found a lot of times the people who disagreed with what I thought had to be the case, later came to regret it because their strategies ended up in failure. I have gotten pretty good at seeing systemic problems, architecting systemic solutions, and realizing what it would take to get them adopted to at least a critical mass. Usually, they fly in the face of what happens normally in society. People don’t see how their strategies and lives are shaped by the technology and social norms around them.