I thought this was about end game tanking, ie raids, not HM flashpoints... But I guess we can talk about generaltities if it makes you feel better.
Intercede is a sure way to start losing mob agro if you go bouncing around to players with mobs on them and you leave other mobs behind... which you are no longer generating hate on.
Suggesting that having Intercede makes the rest "ok" is missing the point entirely.
Is Intercede a good tool? Debatable (I have never needed to use it) and in aoe situations it's a waste of time when all you have to do is target the loose mob and single taunt it.
But losing 15 seconds on our only real aoe taunt is ******** in my opinion.