I have quite a few disagreements here. First is that your setting assumptions matter and can make a huge difference. Assumptions often go without noticing: no obstructions and attack from massive distance both assume there are massive distances... which isn't necessarily true. Consider a setting built with artificial habitats like O'Neill colonies. You could have billions of people living in space with only a couple thousand miles between the furthest residents.

The "no sneakiness" argument is also faulty, not only in a crowded setting, but also in a planetary one. Orbit adjustments while on the other side of the planet mean you might emerge and surprise someone from a new vector. Even interplanetary, if you do a huge burn while at low point around a planet, the burn may go undetected, obscured by the planet - allowing you to change course in a strategically significant way and get a nice Oberth effect boost while at it.

I do agree it is likely to be detected while in transit, if they are looking for you - looking for spacecraft is likely harder than looking for asteroids, and we still discover new near-earth asteroids; it isn't necessarily trivial to find them at all, and then they still need to be recognized as important instead of just a new rock. These things might happen.

Another disagreement: "A fighter shot down in space is almost certainly a dead pilot. " First, shot 'down'.... there is no down! That's important because it changes the survival odds a lot. If an Earth jet gets shot in the engine, it falls the ground, nasty. But if a space fighter gets shot in the engine, it just can't change course anymore. The pilot might be able to sit there for hours or more awaiting rescue.

Well, I could talk about this topic for hours but need to get to bed. Last consideration though is the mission of this fighter: as a missile delivery system, I don't see much use in it in really any situation: long range is better done by a ship and short range might as well just be a naked missile. But perhaps a kind of space fighter would be more of a police interceptor than a military thing, it could shoot to disable engines then tow the disobedient ship away to arrest the occupants...

...and avert danger. Just blowing up, say, a ramming ship doesn't necessarily help. The debris still have the forward velocity and mass to maybe do damage. (of course, spreading it out is likely to help anyway) If you can tow it away in basically one piece, it'd be a lot easier to control the damage and manage the scene. Lethal force might also be outlawed in a lot of cases, so you'd avoid missiles so you can take the occupants alive. Such a craft would be designed around these goals.