As I've said before, MAME is a *document*
It documents the good, as well as the bad, it documents history.
Bad things happen, ignoring bootlegs would be like history books conveniently ignoring WW2. They represent an important part of the story, eg. how the Korean industry came to be, how the official SF2 Turbo came to be, why CPS2 was so heavily locked down etc. It also can document the effectiveness of certain protection systems, which again is part of history (to date *nobody* has figured out Seibu's Raiden 2, and clearly NMK004 was effective for NMK too because all the bootlegs of USSAF Mustang ended up using music ripped from Raiden instead of a clone of the original chip) . Furthermore the information we present can be correlated directly with the stories about how prototype games often got dumped at trade shows and ended up on the markets as bootlegs before the official products (Defender being the prime example, most of the bootlegs are based off the White label prototype build)
If MAME was just about playing the best version of games for free, I'd agree, we should get rid of the bootlegs, relegate them to another build, but it isn't. MAME is about documenting what we know, what we've found, documenting our history. If anything by taking such a serious impartial view of things it strengthens our legal position by making it clear that these are our goals. Once you understand this you'll understand the reasons things are done as they are.
Other emulators, in the past, where the focus is purely on giving you playable games HAVE taken this approach, from memory Retrocade supported just the single 'Best' version of each game, different project, very different goals.
I find the points made by a certain other laughable at best.
Writing about illegal things, documenting them etc. doesn't make the project illegal. The downloads on mamedev.org document what we know, they do not include the actual illegal material.
Furthermore many seemingly original games could well have illegal content. Take the games DoDonPachi II - BeeStorm and Wyvern Wings, both from 2001, both use ripped mod files as the basis of their music, things taken from websites and used presumably without permission (WW has bits of Metallica / Slayer etc. in the music..) Both are 'legitimate' products, but if MAME was to start ignoring everything which could be deemed of dubious legality for one reason or another you'd be surprised at the number of things that got dropped; it would be far greater than the obvious 'bootlegs' and could well extend into popular series' (I believe some later ports of Rainbow Islands can't use the original music because it's such a shameless rip of 'somewhere over the rainbow' the legal departments of the publishers decided against it eg. the Saturn / PSX? versions )
As I said, the role of the project is to document history, not rewrite it or selectively ignore it.
With the ever increasing prominence of MESS in the project and codebase it should also be becoming clearer than ever that the emulator isn't about playing free games. MAME already supports various firmware update programs (pointless if you just want to play a game) but once you open up the MESS side of the code you've got ancient mainframe terminals (with no practical use these days) to built-it-yourself z80 based boards (distributed as schematics + rom in the first place), alarm clocks, eeprom programmers (virtual rom dumping ftw!), car computers (well maybe you could hook it up to the accelerometer on a laptop?), calculators, phones, chess computers, you name it, and while there is some friction regarding some of that code and some members of Mamedev it is still part of what MAME is and what our technology is documenting / running, even if you have to compile it separately for now. Just because these things aren't as widely talked about as some other parts of our project and aren't currently supported in MAME by default (although I expect as the project further matures this will change) doesn't mean they've had any less time spent on them or they're any less part of what we do.
My one sticking support has always been the fact that mame specifically supports bootleg games and the bootleg software they run. Being that you can't really LEGALLY even be in possession of that software outside of a few failed states and 3rd world nations that don't recognize copyright protection so I am wondering how exactly that support was developed and why? Did one of the 10,000 people in Tuvalu who all share the same 1.5 meg internet connection code all the bootleg support? Even if they did, shouldn't that be in a fork from the main development?