Players are already segregated (high level from low level) by current content. High level players are not gonna party with low level players merely because the content they are working towards isn't the same stuff. Only way to effectively make those two groups do things together is to create content that can be repeated for better or additional rewards. Such as: if non-speed run Aurum Vale dropped Darklight bodies, or if helping people through storyline quest gave you multiple elixirs, GC seals or large sums of gil. I think people that believe there should be no segregation between low level and high level players are just too lazy to put together their own groups, or seek out groups with the same skill level.