If you have gotten permission from the copyright owner, then sure.

As long as you bought a copy of the game then I don't see what's wrong with it.

I almost never emulate stuff, but it's not like someone is gonna knock on your door if you do.

I plan to emulate Persona 3 FES over the summer, but I am buying a physical copy too for like $20 brand new so that don't feel morally bad about it.

I don't honestly know about legality. People tell me that it's okay as long as they own they own the original copy, though I'm pretty most of these games have disclaimers reminding them that the IP holder holds the copyright. I know I certainly wouldn't feel confident defending myself that way in court...though I admit I haven't looked into the topic closely.

If you don't own the game before downloading, then I'm sure it's absolutely illegal. I don't know how it wouldn't be honestly.

Morals vary from person to person. I remember back in college, I used to justify it with some of the writings of St. Thomas Aquinas, where he claimed the reason stealing an item was a sin was because the original owner would no longer be able to use that item. In the case of piracy...technically this would be okay...though I think looking back, I was really just trying to justify being a cheap bastard. Now that I can afford to support my hobby, I absolutely refuse to download games illegally, and look on people who justify piracy the same way I look at my past self. Which isn't exactly positive.

Without emulation, countless games of the past would be lost forever.

Emulation is perfectly legal as long as you own the games.

Its never acceptable unless the IP holder says so. PC gamers done care though. MAME pushed on regardless.

Not for recent released games unless you own the game.

Sure, you own the game after all plus the console, nothing more you could do.
Maybe donate some money to Nintendo? lulz

You own a game? Make your self happy and play SMG on Dolphin with all the bells and whistles enabled (if your PC allows it). Connecting Wiimote is also not too much of a hassle, you just need proper bluetooth dongle.

When it comes to emulator itself, from moral stand, it's up to you to decide...for example, if you bought your Wii second hand, Nintendo wouldn't see any money from hardware whether you own it or you play your bought games on emulator...and if you bought your game second hand, they wouldn't see any money from game either.

From legal point...no idea, but this guys have been selling DS emulator for years on PlayStore for $5, and Nintendo either didn't or can't do anything about it:

https://play.google.com/store/apps/details?id=com.dsemu.drastic&hl=en