Military targets are inherently different from civilian targets. Those who attack them should be taken out. But if they limit their attacks to military objectives, they don't really qualify as terrorists. Otherwise all guerrilla warfare would qualify. Or do you think it is inherently immoral to attack your military enemy in a location where he isn't expecting it?
Did you see the Mel Gibson movie The Patriot? By your definition, he was a terrorist.
It is precisely the intentional, indiscriminate targetting of civilians that makes it terrorism. Don't forget, the weapon they chose to hit the Pentagon was a planeload of civilians. That makes it terrorism by my definition, too.
Terrorist are in the business of intimidating and coercing societies and governments for ideological or political reasons. The selection of targets, at least in my view, is not the measure to define a terrorist. A terrorist could push his cause by attacking military targets only, this is of course a much harder prospect than attacking civilians.
No, I have not seen the Patriot. It's just a movie.