The image of a greaser is that of a hood, soemone who is from the wrong side of the tracks, and someone who would do illegal things. Dally fits this description of a greaser and in order to try to stay "tuff" most other greasers, as far as Ponyboy thinks, would follow in those footsteps. The greasers have an image to uphold; they are always being put down by local newspapers, people from the "good" side of town, and their arch rivals -- the Socs. In order for a greaser to stay true to who he is, it is belived that he would have to stay tuff no matter what and this is the persona that Dally exhibits throughout the novel right up until the very end. Therefore, Ponyboy would belive that other greasers would end up like Dally becasue Dally does everything that he has to do in order to keep a tuff reputation and make other people fear him no matter if it's a soc or a police officer. This personallity flaw is also what gets him killed in the end.
well Dally got shot so Ponyboy thinks that the other greases will get shot