Songs Disappearing from iTunes

I've seen other threads on this marked as answered, but they clearly were not based on the posts in them. At first I thought I was going crazy, or maybe had lost some music when I transferred from my old machine to my new one, but now I have songs I know I bought since moving to the new machine that have disappeared. Not just randomly missing songs, but entire missing albums too. Of course, since backing up my music consisted of simply copying the iTunes folder to an external drive (admittedly lazy way, sure) it happily overwrite the folder as I told it to and thus my backups are missing the songs too. This is complete crap, and is NOT answered as the other threads claim. Even if support allows me to re-download everything (at this point, I couldn't even tell you for sure what I am missing since I don't recall everything I've bought) what stops this from happening in the future? If my hard earned money is just going to vaporize off my hard drive at random when I am trying to play by the rules and be legal, give me one good reason not to just save that money and just start pirating everything? Because as much as I don't like pirating, I don't like buying an entire CD for one good song even less, and I like having stuff I bought simply disappear even less than that.

What is the fix for this problem? If Apple lets me redownload everything, where is the proof this won't happen again? I NEED to have a legitimate answer to this question or you and the music industry can kiss my money goodbye. Limewire will be my new music source.