system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some people find GMO controversial when farmers have been modifying crops for centuries?

So, my understanding is that corn is a perfect example of a GMO, since it has been selectively bread to increase yield.

Why is there a modern push away from GMO?
gpt
There are several reasons:

* There's an aversion to food that "comes from a lab," as it were.
* Selective breeding is generally between crops that are the same or very similar. Genetic modification allows traits from other species to be incorporated into the crop (if you want a tomato that doesn't freeze in a cold snap, you could take genes from a fish that lives in frigid Arctic water, for example). That freaks people out.
* GMOs are largely controlled by a handful of corporations, the most notable of which is Monsanto. These are companies that people aren't too fond of, and they use some pretty heavy handed business tactics to shut out any smaller competitors.

*Edited for word choice*