Well the double-whammy is that they *love* their Supers characters. Rifts is a hard sell for half the group because of their pre-conceived notions about the setting, largely from watching those old Flame Wars from the Palladium threads and everyone's non-contextual horror stories.
Anyone that's played Rifts natively for any amount of time knows differently. I think some of them are skeptical of the sheer Gonzo nature of Rifts. Which is weird given the Gonzo nature of Supers in general. So my plan is to CROSS THE STREAMS!
All those horror stories seem to be made up out of whole cloth, and anything over at RPG.net that involves Palladium seems to devolve into some beatdown about how bad the system is, all while pretending to ignore it's really just house-ruled D&D. I think the true nature of Rifts for me is that even though there is so much evil, horrible shit going on with demon lords and vampires and alien intelligences in a completely devastated post-apocalyptic hell hole, most people haven't given up hope. It's by far the least nihilistic approach to the genre, and as you correctly point out, matches with superhero stories very well.
RE: superheros, when the Conversion Book came out, being a bunch of teenage boys everyone wanted powers of course, so we all created alts for our campaign. I ended up with a vagabond who had invulnerability and a strong distaste for the Coalition. That character was nothing more than the most obnoxious jackass ever, constantly getting the characters into trouble, never fully understanding that lasers and bullets and missile and whatever else HURT everyone else.