Sylas is like Urgot but with better motives.
Urgot's a social Darwinist who wants to create widespread bloodshed and destruction so that the "strong" will rise to the top and...I'm not sure what step 3 is here. Create a better society or something. Anyway, Urgot's got a classical Noxian view of "The strong prosper and everyone else doesn't matter."
Sylas is coming at it from the other end. He wants to free the downtrodden mages of Demacia so they stop getting murdered for being born wrong. He doesn't seem to care about strength or weakness, just the basic decency of not killing/oppressing people for circumstances beyond their control.