Some people don't like playing one or the other, but want certain items that require certain modes to be played. A great example of this is I like playing PvE a lot more than PvP but want Dead Orbit armor. I could either run loops for a long time collecting materials to trade in for Crucible Marks, grind ranking up my Dead Orbit reputation and hope I get the armor from the rank ups, or grind the Crucible. Same thing applies to the Vanguard Marks. You can't get them unless you play something other than Crucible while wearing non-faction class armor items. Would you like if we could trade marks? What do you think?