One of the reasons I'm adamant about native Bitcoin being used and seen as a 'reserve currency' rather than and 'exchange currency' is that it would not as terminal event for the system to go through a longish period of turmoil.

If sidechains were in the picture it would complicate things hugely for 'the cartel' for a bunch of reasons.  Chief among them:

 - Sidechains would have a variety of methods of functioning making it a real challenge for a 'cartel' to target the soft-points of each one.

 - Many of the sidechain implementations probably would have gone back toward an architecture which values and derives support from individual users.  Native Bitcoin has gone a long way in the opposite direction in my observations over the last 4 years.  Anyway, this individual contribution factor of sidechains could provide some support to the native Bitcoin backing and give the userbase (your 'rebels') at least a little bit of firepower against 'the cartel.'

 - Sidechains would be operated and valuable as independent solutions to individual coalitions.  The main interest in native Bitcoin to each of these would be that it remains universally credible in order to provide the backing they need.  This would probably translate to native Bitcoin ending up in a form which does not align with the end-goals of 'the cartel'.

 - Sidechains would have individual participants and operators who were highly technically competent and motivated.  These people would naturally be operating at the 'nexus point' between the sidechain and the native Bitcoin backing store.  What this means is that correct technical decisions would be made quickly, and interference at the 'nexus' level would be countered by people who know what they are doing.  Also, of course, a population's worth of transactions from a sidechain would be aggregated into a handful on the native Blockchain level transactions.  This would offer both the efficiency which might be needed under some attacks, and also a 'big stick' which has use politically.

Lamentably, I have to agree with Jorge that on the current trajectory with a zillion tiny and dis-interested users following whatever their Multibit UI is showing them, there is a strong possibility for a successful subversion by a 'cartel'.  Or not even that so much as simply a natural progression to a solution which doesn't have much good to offer.  It's why I'm so negative about Bitcoin being cast as a stand-alone exchange currency.