The outrage stems from a comment Bay made about his upcoming live-action flick at a recent media event .... in which he said, "These turtles are from an alien race, and they are going to be tough, edgy, funny and completely loveable."

Of course, TMNT fans are FLIPPING OUT ... since everyone knows the turtles mutated during a brush with radioactive ooze after falling through a sewer ... duh.

One of those angry fans is voice-actor Robbie Rist ... who recently posted a letter to Bay stating, "You probably don't know me but I did some voice work on the first set of movies that you are starting to talk about sodomizing."

Rist added, "I know believing in mutated talking turtles is kinda silly to begin with but am I supposed to be led to believe there are ninjas from another planet? The rape of our childhood memories continues ... "