If you were able to make atomically accurate copies (including software) of the latest car that Ford were trying to sell and for less money than they could sell it for and maintain R&D, then you would lower the value of that model of ford down to the cost of copying it after a while, as you'd probably be selling them for around the production cost of about £2-3K rather than the 20-30K they currently charge (and that's for a fully specced model). However you wouldn't have deprived Ford of any stock at all. It could also be argued that most of the people that bought your copy wouldn't have bought an original Ford anyway due to the cost. However in real terms, the value of Ford's new car would in fact plummet to match the cost that you could produce it for.
In digital media the same is true, as almost everyone agrees that the people that do the work of producing the music deserve to be paid (song writer, musicians, sound crew, editors, venue owners (where it was recorded), etc.). Some of these people will be paid up front (sound crew, and venue), which means that these costs have to be recouped before the song writer, musicians and editors start making any money. If they had to take out a bank loan, then this needs to be paid every month.
Now standard business logic says that your break even point is the point where money coming in from the items you've sold matches your costs to produce and sell those items (whether it's cars, cokes, buttons, or music) (google break even chart for an explaination).
If our mythical 4 person band is selling through Apple, then they've got a fixed price point of around 99p/song and apple take about 30% of that (let's call it £1 and 30p for easy maths) so the song produces 60p towards covering expenses. If a sound crew of 5 people costs £35/hour/person and a song takes 1 hour to get right, then that means that the cost of the crew is £175, which means that JUST to pay their wages you need to sell 292 copies of your song on apple. Doing a quick google, a recording studio in London charges between £30 and £90/hour so if we go for the mid point that's £60 which is another 100 copies (bring our total up to 392). And this is just for the fixed costs of producing the initial recording. From the same website that I got the cost of the recording studio, they also charge £130 for mastering (which I assume is the production of a master copy that is a high enough resolution to create any feasible subsequent copies from). And £130/hour for post production. So let's assume our band doesn't have someone that can so the post production, and they don't own their own mastering software/hardware, that's another £260 minimum added on which is another 434 sales (bringing our total up to 826). Once they've sold those they then start making money to pay the people they didn't have to pay up front. So if the band needed to practice the song for 30 hours before it was ready to be played and they "pay" themselves £10/hour then that's £40/hour for the band which comes to £1,240 (1 hour to produce the song) that needs to be covered by the music, which is another 2067 copies (bring our total up to 2893). The editor/manager probably charges around £20/hour (plucked from thin air with no research what so ever) and spent 4 hours arranging thing and making sure the recording happened properly. This is another £80 that needs to be covered which is another 134 sales needed (current total 3027). And finally the song writer also likes to be paid £10/hour and spent 6 hours (being nice) writing the song which is another 100 sales (current total 3127).
So Just to cover the cost of selling their song on apple, our band needs to have sold 3127 copies of that song. If that song doesn't do very well and they only sell 1500 copies then they need to sell an additional 1627 of other songs after covering the costs of producing those songs to break even.
So, no copyright infringement isn't theft, however it is still depriving someone of the income to for the work they've done.
I suppose we could always go back to the days pre recording, where if you wanted to hear music you had to actually hire the musicians and pay them up front for their work, but then how many people would be willing to sacrifice their music libraries for that?