I found it upsetting that 5 of the 6 people used the argument that the games are no longer available and that therefore the developers are not losing any money as their excuses for pirating roms.
First, because it's irrelevant. It's up to the people that made the product or the people whom they transfered their rights to whether or not the product should be available to not. To give a clear example, someone could make a game available for a limited time only on purpose, that doesn't give you a right to pirate it if you didn't get it during the time it was available.
Second, because it's false. Companies are still making money off their old games. Nintendo was brought up several times but Nintendo in particular has been making their games available. One, through GBA games (Mario 2, Mario 3, Yoshi's Island, F−Zero) are all available. Pirating a rom is directly influencing whether people will buy these products. Why buy Mario 2 for GBA if you already downloaded the ROM for free?
One arguement would be that you already purchased the SNES cartridge. Fine, in that case either play it on your SNES or in this particular case you could argue a ROM file is okay for *you*. That does NOT make it okay for someone that has never paid for the original cartridge or has since sold the cartridge to someone else.
Also, Nintendo has been using older NES games as bonuses in GC games. For example Animal Crossing has several NES games available as bonuses. Clearly Nintendo put that feature in because they thought it would be cool and therefore increase sales and also give the player rewards inside the game. But, if you pirated the ROM then clearly it's not a plus for you and you are less likely to buy AC. Again taking money from Nintendo because you pirated a rom.
Finally, in this world of Java enabled cell phones, companies are using their old titles. I can play PacMan, Mappy, Space Invaders, Pengo, Scamble, Tetris, and hundreds of other games on my cell phone. If I instead pirate the roms, why would I need to buy the cell phone version? Especially when in a couple of years the cell phones will be fast enough to run the emulators. Again, the excuse that these titles are old is irrelevant. They ARE still being sold and if a particular title is not being sold today that does not mean it will not be sold tomorrow.
On the other side of all this, to Matthew Cinquemani, I know exactly what you mean about them not feeling the same on a PC. Try playing them on an XBOX. In that case, at least to me, they do feel almost exactly the same. (PS: I have not played any emulated games on my XBox for which I do not own the cartridge)