Dunno about the perfect sound forever, but they are certainly the exact same sound forever (assuming no scratches). It's worth keeping in mind that the CD spec was written in 1980 when 16-bit audio was difficult to comprehend technically. Sony/Philips wanted to use a wider data word or higher sampling rate but technology at the time meant that the disc would be huge and the hardware requirements unmanageable. They compromised that a 120mm disc at 16-bit, 44.100KHz would be reasonably good sounding for a majority of people, be portable and fit a standard recording of Beethoven's 5th.
It's hard to argue that it really is a successful medium, sounds much better than cassettes, less prone to damage than vinyl. It does sound fine for 95% of people (most of whom think MP3s are OK, though) and even for many of the 5% audiophile it's usually tolerable at a party or in your car. It's like anything, the sound can be tailored to the medium, some CDs really do sound terrible if the levels were wrong or the mix was targeted for vinyl. But OTOH I've heard some really lousy LPs lately because the punk kid engineer was used to mixing for a CD and the sound was muddy. I also have a really terrible sounding Springsteen LP that is vintage, I bought it in 1984 myself. I never realized how bad it sounded until I got a decent table.
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“Anyone who believes in indefinite growth in anything physical, on a physically finite planet, is either mad or an economist.” -- Kenneth E. Boulding