system
Given the following post, respond as if you're commenting on Reddit:
human
[Ghostbusters] Before the Ghostbusters are formed, why do Ray & Egon consider Peter to be a part of their "group"?

He is apparently a con-artist who is only in academia to get into the panties of college girls, and also appears to be (before proven wrong) an ardent skeptic to the existence of the paranormal.
gpt
He's their friend, they hang out with him because he can help them get girls and he acts as the face for their research. His skills as a con artist can help them talk the university into giving them funding. 

And Peter hangs out with them because they put up with his bullshit and helps him maintain his academia cover. He also knows how smart they are and it's wise to stick with them to benefit from that.