In the first handful of pages you have terror weapons being used on Skinnies, something to the effect of "I'm a bomb and will explode in 30 seconds". Tactical nuclear weapons being shot off left and right. Just with the opening I don't want a future where these are valid military tactics.
I disagree. One of the points in the book was that the Terran military does have the power to obliterate whole cities from orbit (in the same way the "Bugs" obliterated Buenos Aires) but instead of doing so, they use infantry to make the destruction more selective. Right in that scene you describe, Johnny Rico says that destroying the city's waterworks is exactly the sort of thing they are supposed to be doing... it will be a massive headache for the locals with few casualties.
As for the bomb, you may call it a "terror weapon" but I put it in a different class than what we usually call terrorism. Terrorism is cutting off heads and burning people alive and crucifying people with cameras running... blowing up small children, slaughtering civilians in a deli, slaughtering shoppers in a mall, and so on. A bomb that advertises that it will blow up soon, in the locals' language, allows the locals to run far away before it blows up. Johnny Rico said the thing would give anyone a nervous breakdown (or something like that) but it's not remotely in the same class as the horrors we call terrorism.
Also, in the 50's, people believed that tactical nukes would become a battlefield staple. It was a science fiction novel; it's not surprising that it imagines tac nukes having a place on the future battlefield. In the book, most of the infantry didn't have nukes; Johnny Rico had a few, but only because he was an officer (a very junior one). Most of the bombs were simple explosive devices. And keep in mind that this was written not that long after World War II, where the normal course of things had airplanes unloading entire cargo bays full of bombs on cities. As I said earlier, Heinlein was imagining a precise application of force, and at the time that was a pretty science-fiction idea. (These days, American troops can call down a bomb or missile that can hit a single building and leave the buildings around it untouched. That's actually pretty amazing when you think about it.)
One of the core concepts of the book is the franchise is only available through Federal service.
Yes. The narrator protagonist, Johnny Rico, only wanted to serve in the military; but there were other options. His friend wanted to work in a research lab, and since the friend was brilliant, he got his wish. His other friend, a female, wanted to be a starship pilot and got that as well.
The basic idea was that by serving in the government, you showed some ability to put your needs second and the needs of the many first.
So in order to vote you must be indoctrinated into the government and there is no concept of loyal opposition.
Your biases are showing. "indoctrinated"? "no concept of loyal opposition"? I claim that these are not valid statements, and if you want to stand behind them, please cite which chapter illustrates each point.
I don't recall the exact name, but everyone was required to take a class along the lines of History and Moral practices.
"History and Moral Philosophy" They were required to take it, but not required to pass it and indeed I don't think received a grade for it.
My high school had a class called "Civics" that was not completely unlike this class, but I had to pass it. Are you horrified? Is that "bleak"?
One thing that has always stood out for me in those sections is the concept of total war.
Yes. I think it's fair to say that Heinlein believed in "total war", as so: Don't get into a war if you can help it; but once in a war, fight to win. I personally agree with this idea. Don't send our soldiers to die in penny packets; either don't send them, or send so many that they roll over everything in their path. Personally I'm a "live and let live" kind of guy, although it troubles me to think about the Islamic State throwing gay people off of buildings and all the rest of it.
Again I may have the specifics wrong, but the teachers makes a comment about "ask the leading fathers of Carthage how war never solves anything"
A student made the comment "Violence never solves anything" and the teacher used Carthage as an example of how violence had permanently solved something. Note that the teacher never said that what Rome did to Carthage was moral.
In the book, the "Bugs" attacked human colonies with the specific plan of killing every person and taking over the planets. (Johnny Rico said something about "they like the same kind of planets we like".) Therefore, in the book, there was no chance of simply negotiating a peace with the "Bugs". They started the war, they intended to prosecute the war, and the only way to stop the war would be to render the Bugs unable to continue. For that specific situation, violence was the only way to solve the problem.
Also in the book, an alien race known to humans as the "Skinnies" was initially allied with the "Bugs", but convinced (in part by that raid you didn't like at the start of the book) to ally with the humans. The humans did not exterminate the "Skinnies" and I didn't get the sense that the humans were planning to exterminate all the "Bugs".
Implying that wiping out your enemies is not only a valid tactic but is the best one.
Not in the book. You brought that yourself.
And I'll say again: the humans preferred to use the Mobile Infantry to hit exactly what needed to be hit, rather than smearing whole cities at a time from orbit. If your assertion was correct, why did the humans bother?
I think there was a single throw-away reference to a bomb of sufficient power to crack a planet open, but humans never used such a thing in the book, and there wasn't any dialog like "gee I wish we could just destroy this planet and kill every Bug."
A key message throughout the book is that the ends justify the means, that to me is bleak.
Not in the book. You brought that yourself.
If you want to stand behind that, please cite a chapter that supports it.