If you look through the comments here, you'll see several people specifically mentioning agent orange as what's wrong with Monsanto.

A lot of the current activism against monsanto is due to pressure groups who have hated them for a very long time. Greenpeace and Friends of the Earth (both of which I used to be a member of until I realised what anti-science crap they were spouting about GMOs) have both had long-running campaigns which have strongly affected the public mood about GMOs. The 'Frankenfoods' Greenpeace campaign set the UK down a particularly crippling path.