Well, let's be real.
Someone talks about Dolphin:
It's highly possible that they own the disk, and highly possible for them to have ripped it themselves, even though it's fairly improbable that they statistically did.
legal score card: (2 yes, 1 no)
Someone talks about a NES emulator:
It's highly possible that they own the cartridge, but highly improbable that they dumped it themselves considering technical needs.
legal score card: (1 yes, 1 no)
Someone talks about MAME:
It's highly improbable that they own the arcade machine, highly improbable that they dumped it themselves, and basically inconceivable that they would really have gone through the trouble to do so were they to have the cabinet anyways.
legal score card: (0 yes, 3 no)
Point:
MAME is probably the most freely discussed and accepted form of copyright-violating downloading for video games across the internet - referenced openly in many locations by noticeable people within the industry - and also the most direct and obvious way of admitting that you just downloaded a ROM illegally.
The tolerance seems mostly surrounded by the simple facts that there's really very few chances to play these games without the emulator's assistance, a prohibitive cost structure associated with authentic ownership, relative scarcity of functional equipment, abnormal space requirements needed to maintain, and a collector's market barrier to owning them legally.
Doesn't really change the facts of the matter regarding what's going on.
Still, I bet if you really pressed toward an honest and off-the-record discussion, most people who are enthusiasts not only use it, but do so without any guilt or remorse, due to some combination of the reasons states above.
Just my thoughts on the matter.