Guilds are your LFG tool in PvP with the same logic. In fact it´s even more so since a premade PvP group with voicecom simply destroys opposing random groups while even a bad PvE random group will usually succeed in a flashpoint after a few wipes.
I still read people swooning over how awesome WoWs PvP community was after release where you knew your enemies and every match was hard-fought.
Yet nowadays LFG Tools are somehow perfectly accepted in PvP but are the absolute evil in PvE.