It is illegal, in every case where the artist has not explicitly made mention that they are okay with the sharing of their music.
Immoral? Completely different question.
I don't think so, not at all. Record labels and musicians used to the old way of doing things are just butt hurt and not being able to make as much money as they used to, because record sales has been severely impacted. The music industry will never die because of piracy. Not so long as there are people passionate about music, so really the industry isn't at threat. It's merely a new market and musicians need to find new ways to make income, the paradigms for money making have merely shifted.
Not that big a deal, because at the end of the day, if you're a small artist, you want as many people to hear your music as possible, and if you're a huge artist, ♥♥♥♥ you for being so greedy. ♥♥♥♥in' Metallica.
Yeah, its a fact that its illegal. There's no disputing that. Even if it is no longer available commercially.
As far as morality goes, I agree with Saul. The ways money will be made on music is shifting from the album to touring and I believe that's beneficial to the medium and will cut down on superfluous song/ album releases that are merely cash grabs. That is not to say that other people should be able to profit from their work. Commercial piracy should still be illegal, but piracy for personal use should not.
If there's an album out there, that isn't available to purchase any more, is it illegal to download it?
Legality aside (because I don't know if there's ever a circumstance where piracy could be "legal"), I've often downloaded out-of-print or otherwise unavailable recordings or b-sides from artists I like. Old recordings, live bootlegs, and b-sides all sort of fall into this area. If I could pay for these recordings, then I would, but if I actually am not able to because they just aren't available for purchase, then I don't feel like going without if they are available extralegally. But that's just me.
and, if I own an album, but when I put it on iTunes, it's not the quality I want. Is it illegal to download a higher quality version?
This I'm a little unclear on. If you have the physical album you should be able to rip it to any bitrate quality you want. If you bought a digital version, then most artists give either multiple options for what bitrate or file type you want.
If you still somehow ended up with a poor quality version, but you've actually purchased the album already, then I don't see the problem with getting yourself a higher quality version. In the old days if you ruined a tape or a record you'd have to buy a new copy, I suppose, but in the digital age I don't think that's an appropriate expectation anymore.
In general I always try to support the artists I like by compensating them for the music I consume. I always try to buy directly from the artist, whether I'm buying digital or physical copies of the music, by buying directly from the artist's webstore or digital retailer of their choosing (eg Bandcamp). I only use the iTunes store as a last resort, because I don't like how big a cut they take as a retailer. If I'm buying physical then nine times out of ten I'll be preordering from the band themselves.