Have been rotating 29'' Trinitrons for more than 10 years now. At most, I defocused one due to this repeated-ad-nauseam process. Nothing you can't easily repair or substitute, for that matter. But sure -- not everybody can/wants to do it due to many reasons. That doesn't make of displaying a game for 3 : 4 in a 4 : 3 set anything less than an aberration, though, from any point of view -- visually, mechanically, emotionally, even.
Dont know what you are talking here, but there are many games that are interlaced and not only their intro-screen.
There are a few, not "many", and, saving very exceptional stuff like some ST-V titles, they respond to a moment when the principles weren't totally set -- that is, American developers doing some experimentation, to put it in kind words. There's a point in emulating all this with an interlaced picture which has to do with purism, nostalgy and whatnot, obviously, I'm not denying that. But since you're asking, I'll also say there's a bigger point in restoring the visual consistency of these games' graphics, much like when we run VGA MS-DOS games designed at 320 x 200 at 15-kHz. And the emulation allows you to do it. Just try, say, MAME's Columns '97 in a 31-kHz CRT and you'll know what I'm talking about here. (Or maybe not.)
The main aim of GroovyMAME are CRTs and every CRT is capable of displaying interlaced stuff.
So what? Are you missing that there're 24 and 31-kHz (and beyond) CRTs? Anyway, I'd never advocate less features for GM or something (!), don't panic; just encouraging people who went all the way to have a dedicated CRT at home to re-think their habits and their original motivation with the games for a 3 : 4 display.