Realism is viable so long as you only want to do realistic things. Exploring space is realistic. Mining it, colonizing it, or fighting Epic Battles in its far reaches are all operatic things. None of them is impossible. But all are highly unlikely, at any rate in the readily foreseeable future, given technology as we know it.
In fairness to me, I have generally discussed the 'plausible midfuture,' a time and place that is characterized as plausible, but not necessarily most likely, or even very likely at all. But that doesn't do away with the problem. Does an implicit requirement for 'plausibly' demi-realistic technology amount to an unrealistic constraint when applied to essentially operatic settings?
Or, putting it another way - and bringing it down to cases - given that deep space warfare is pretty damn unlikely under the technological restraints I have discussed here, does the Space Warfare series really provide any useful help for writers or gamers who want to make their space battles more convincing. Wouldn't they really be better off to adopt the operatic technology of their choice, then work out the implication for combat under those conditions?
This came up in a recent comment thread, in which John Lumpkin's novel, Through Struggle, the Stars, got taken in vain. I have not read the book, so I have no informed opinion on how convincing his setting is. But the question raised is much more general - does putting 'realistic' spaceships in a setting of space colonies make it less plausible than allowing a technology that would justify deep space travel as convenient and cheap?
As I have noted here before, my bias toward realistic-style spacecraft (and other details of a setting) is essentially aesthetic. Magitech is inherently arbitrary. It is well done if it holds together with internal consistency, but it is still arbitrary. And just on the level of purely visual aesthetics I was heavily influenced by the early space age, when we started getting pictures showing how things in outer space actually look.
Oddly enough, by the way, I have never seen Hollywood successfully capture this look, especially the brightness of spacecraft in full sunlight at 1 AU. In some cases this may be because Hollywood loves gothicism in space, but I suspect the real reason is much more basic: No studio lighting is anything near as bright as direct sunlight.
(Although APOD doesn't mention it, the dim lighting of the spacewalk scene above suggests that it was taken while the ISS was passing over Earth's nightside, illuminated only by floodlights and sucy, not direct sunlight.)
Speaking of Hollywood spaceships, the Venture Star in Avatar may not be quite as realistic as it looks. Its appearance, with big radiator wings and so forth, is very much Plausible Midfuture, suggestive of a gigawatt-output nuclear electric power plant ... but the drive is capable of reaching relativistic speeds at more or less 1 g. I'm not gonna do the math here, but that drive is putting out waaaaay more than a gigawatt of thrust power. Those impressive-looking radiators couldn't shed much more than the ship's galley heat.
See? This is the sort of problem you get into when you start running the numbers for our favorite space scenarios. And the problems exist at multiple levels of meta-ness, from the sorts of technical issues I just mentioned up to (at least) the question of what relationship science fiction settings can or should have to 'the future.'