They did not hate the urban elite of Cambodia for no reason at all - this was a French-created and 'Frenchified' elite that had long lived parasitically upon the rural poors.
The Khmer Rouge leadership mostly hailed from the same class anyways. Of course, as in all these purges, the most dangerous thing to be in Democratic Kampuchea was to be a Khmer Rouge cader...
Oh yes. Oooh Yes.
No. That's not the way the Khmer Rouge got created.
It wasn't just 'independence'. Sihanouk was pretty good at playing out his neighbors against each other and keeping his country out of the worst of the trouble for twenty years, until Nixon went for Cambodia's collective neck with a vengeance.
Of course, Sihanouk was also a brutal dictator...
The same people who supported the Khmer Rouge during the 80s, ironically enough.