They are placeholders, not final art. I've been working on a game, and I rip sprites from wherever I find them. Not because I am a callous thief, but because the art is temporary until I can get a prototype, and convince an artist to join.

You might use them as placeholders, which I have no problem with, but that quote clearly implies using them in shipped products.

"first few simple games" ≠ "shipped products"

Not to say that stealing other's content is okay, but I could certainly understand "borrowing" images to use in games when you're just starting out. I actually think it's usful because you can make clones of your favorite games in order to learn how to program.

Not a lawyer, but using a couple of sprite rips in the process of learning sounds like it ought to be fair use to me. Are you a lawyer?

It may be fair use, if you do not distribute the game. Once you distribute it, all bets are off, and fair use would almost certainly not apply.

Many media companies have staff lawyers to police their IP, so it does not usually cost them any (additional) money to send out copyright notices.

So presumably you're against fanfics and sprite comics too? As with everything that can be copied (digitally or otherwise) and used in derivative works, fair use et al. concerns apply. (Hence the other commenters noting that it's common and fine to do this for self-education.)

That's not how fair use works. Simply making a derivative work is not enough to take advantage of fair use. The derivative work must fall into certain categories of use. A lot of fanfic and sprite comics would not fit into fair use, though many would. It is a very fact-specific analysis.

Indeed, I don't think I accidentally made the assertion that being a derivative but original work was sufficient. Similarly profiting off your work does not automatically dismiss any fair use claims.