It is not added to food, it is an herbicide, and in levels used is found harmless by studies. The scientific concerns about it are the same as with most herbicides and pesticides, that those exposed to large quantities repeatedly over the years (some farm workers, herbicide workers, etc.) do have increased cancer risk.
And it has nothing to do with aspartame.
To learn more about Roundup (glyphosate), start at the wiki page and go to the linked cites to learn more.
https://en.wikipedia.org/wiki/Glyphosate