The alternative is copper and cPVC. cPVP is just another plastic. Copper leaches copper into your water (though not harmful for most purposes), and is attacked by common water ph to corrode and ultimately break requiring replacement (though this takes about a lifetime). Copper is more expensive - 10 feet of copper pipe will cost as much as 100 feet of pex, and you have to join the copper every 10 feet: more expensive labor.
The claimed worry is impurities from manufacturing exposes workers to them when the pipes are first turned on. Note that there is no particular reason to believe those objections do not apply to approved pipes. My opinion is they don't like the idea of pex because it is less labor which means less money for them.
I personally use pex for all my plumbing in my house. It is cheap, quick and easy.
You say that copper will eventually corrode, but how does that compare to the lifetime of Pex?
PEX has essentially zero resistance to UV, in sun exposure salutations you get a few weeks of lifetime. Most buildings don't expose plumbing to sunlight though. There are a few (very few) chemicals that attack PEXs, but all the ones I know of are nasty enough that I'd wear full protection if I ever have to work with them - not something I expect drinking water will ever contains. Pex is resistant to any PH I'd want to drink.
