OK, if you are asking whether or not to mix with the local...HELL NO!! If even a smidgen of them assaulting the national is true then absolutely NOT!!! There's more than legal consequences for their actions, and I for one would not want to be associated with someone who seriously beats someone else. (OK, small fistfights will happen, but 2x4's?
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If you are asking about mixing with the national, that's a little more vague. Depends on how much of the conflict their egging on, starting, etc. If they are not acting very "fraternal" to the other groups and trying to start stuff, then I don't think they should be getting the attention of some very lovely ladies. Plus, if they are into some shady stuff, I wouldn't want to be anywhere near it. (Guilt by association, ya know?)
It's up to ALL of us to keep the Greek system afloat and improve the bad reputations we are sometimes given (some with reason, some without). If we take a stand and deliver the message that we will NOT socialize with Greeks who aren't living out the Greek ideals, then it will hopefully improve the system as a whole. "If you ain't acting right, then I ain't playing with you!"
(Another way to look at it. . .If you had mixer shirts made, would YOU be proud to wear their letters? Would you be proud to see THEM in YOURS?)