I followed the sidechains AMA.  Nothing new in that story at all, and nothing whatsoever which would support much of what you've been saying.

I will say that I'll expect sidechains impact on alts to be one of 'separating the wheat from the chaff.'  I believe that a fair number of alts were created to address some legitimate and valid needs that the the designers felt important.  Probably a majority of alts were created as pump-n-dump scams.

Alts which were created for the right reasons probably largely lamented the fact that they could not let Bitcoin do the heavy lifting as the actual value component.  These should be absolutely delighted to switch to a sidechain implementation.

OTOH, I foresee howls of rage and despair from those alts which are pump-n-dump scams designed with the hopes of making some early adopters rich.  I suspect that a fair amount of the negativity toward sidechains is from this corner right now because I can see no other legitimate complaint against sidechains.  This from a risk perspective, economic perspective, philosophical perspective, or any other rational perspective.  At least not one that is based on any skin-deep understanding of things.  (Actually, I take that back; those desperate to destroy Bitcoin as an empowering technology for individuals will also be quite alarmed by sidechains.)