Our alums are our brothers. They're constantly there to remind us that we have to get business done! I think when you go out into the real world this all becomes more clear
But as to lack of respect... That's absolutely despicable. The alums of your chapter are just as responsible (and probably more so) for your being able to call yourself a member of XYZ today!
Treat them with the same respect you would want to be treated with yourself -- or get the hell out!