It's funny, but I don't recall ever seeing any arguments on the Fallen Enchantress boards about dragons not being scientifically possible. I wonder what's behind all the apparent huff over fighters in Galciv.
Fallen Enchantress isn't in a genre that has "science" in the name, nor is it in a genre which is considered particularly likely to have some basis in real science. Not that that necessarily means much, but there is an expectation that science fiction makes some use of science fact (though how much is another story), and that expectation results in discussions such as this. Also, as far as these types of discussions go, this one isn't too bad.
I personally neither support nor oppose the inclusion of starfighters, as it is only a game. and as long as it makes a reasonable amount of sense within the game universe I don't really care. I do nevertheless find these kinds of discussions amusing as long as they don't devolve into pissing contests. And, in my opinion, given the game's size claims for Tiny-hull vessels in Galactic Civilizations II, we already had starfighters, they just weren't the short-range kind that require carriers to reach the combat zone, and this would tend to suggest that battles in Galactic Civilizations II occur under a set of conditions which at least allow fighter-like vessels to be useful.
1) Difficult, if possible at all, because our knowledge of science is incomplete and is continually changing, with us receiving surprises and shocks to our understanding almost on a daily basis.
The greatest difficulty in writing scientifically-accurate stories, at least as far as the current understanding of science is concerned, isn't so much that our understanding of science is incomplete as that many of the people writing science fiction are not well-acquainted with science, as many of them have not pursued professions in a technical field. Then there are the kinds of things which go on in works like Star Trek, where the writers sometimes choose to ignore real science because real science apparently makes the plot less interesting. This isn't necessarily a bad thing, of course, but it can lead to some implausibilities, such as how in Star Trek ejecting the warp core is apparently the solution to about half the problems a starship can encounter.
Space fighters are cool staples of science fiction, and based on this, I think they should have been introduced long ago whether or not they make sense according to what we presently perceive as science fact.
I'm rather ambivalent on the use of other works of fiction to either support or oppose the inclusion of anything within a specific work, if said work is not set within the same universe as those other works. I'd much rather see arguments based upon the known characteristics of the setting and, since Galactic Civilizations is science fiction, also based in real science (or at least the subset of real science which is applicable to the setting). Since Galactic Civilizations is a fictional universe, deviations from real science are excusable and expected. However, that the conditions or technology in Universe A are right for some specific aspect of that universe to be reasonable does not imply that the conditions or technology in Universe B are right for the same technology, as this isn't really any different from saying that since magic cannot create food in the Harry Potter series then magic cannot create food in the Death Gate Cycle. The universe of Galactic Civilizations is fundamentally different from the universes of Star Trek, Star Wars, or any other science fiction setting you care to bring up, and while all of these are (presumably) working off the same basic ruleset (some shared subset of real science), the way that the "superscience" works (i.e. the stuff which isn't part of real science) need not have anything in common between the settings. This is a significant flaw when basing an argument for the inclusion of a superscience feature of one universe in another universe on that feature's existence within that other universe or that feature's existence within any number of other universes, as the superscience of one universe need not follow the same rules as the superscience of another universe (regardless, it would be nice if the superscience at least followed consistent rules within its universe, which isn't always the case, at least in any readily apparent manner). That "everyone else" is doing something is not, on its own, a good argument for why I should do that thing (not to mention that there are a number of reasonably good works which do not include starfighters, which could be brought up to counter claims along the lines of "everyone else" has them).
I will say, however, that Galactic Civilizations II appears to allow for starfighters, as the Tiny ship hulls are of a size appropriate for fighters, and under the assumption that combat takes place without the use of the superluminal drives and that carriers are not too much of a liability within a fleet, I see no apparent reason why a Tiny hull with the full hyperdrive and long-term life support rig that Tiny vessels in GCII include would be viable while a Tiny hull lacking the full hyperdrive and long-term life support rig would not be viable (this is, however, ignoring arguments about the viability of the Tiny hull in GCII, and the relatively low viability of the Tiny hull in GCII relative to the larger hulls is a potential argument against the viability of short-range fighters similar in scale to Tiny-hull ships within the universe of Galactic Civilizations).