And is’t not to be damn’d, To let this canker of our nature come In further evil?

Slippery slope, this.
I mean. Morally, yes.
One fully understands why killing Hitler before he can kill anyone is a perfectly acceptable thing to do. It does feel moral to kill a killer like him before he can kill.
But to be damned for it?
Let’s say you had a chance to kill Hitler and you didn’t do it. You wanted to. You felt it was the right thing to do but your stomach turned so at the thought of murder, that you failed to turn the knife. Would this God punish you for such a failure?
I mean – it seems to me that the law of the religion is pretty clear. It’s “Thou shalt not kill.” Period.

Not – ‘Thou shalt not kill unless the person you’re killing is a villainous killer, in which case you are obligated to kill. So don’t kill unless you really have to and if you really have to and you don’t, then you’re looking at an eternity in the damnation machine. Clear?”

He that hath kill’d my king and whored my mother, Popp’d in between the election and my hopes, Thrown out his angle for my proper life, And with such cozenage – is’t not perfect conscience, To quit him with this arm?

It is rather a long list of grievances.
Claudius has really done some A+ work as a villain.
The phrase I’m most interested in here is the one about popping in between the election and Hamlet’s hopes.
First, because this is one of the most explicit references to the question of succession that hangs over the play but is rarely addressed directly.
Second, the “election” sounds like a democratic process but it is certainly not in this case. In fact, it illustrates how we got such a word as election and how its roots are in powerful men choosing a single powerful man to be their figurehead – and it is that way still in so many ways.
Third, popping is such a light word for what the results are. It is an interesting choice for the action. Claudius just pops in where Hamlet should have been and the whole succession committee was like, oh, it’s you? Oh, okay – fine. Next order of business!

Why, what a king is this!

This is a very odd moment for Horatio to exclaim like this. He’s not really directly responding to what Hamlet just said; Hamlet was just talking about Rosencrantz and Guildenstern and only obliquely referred to Claudius, if at all, as one of the mighty opposites. (Maybe.)
So…this exclamation from a man who mostly just nods along and supports Hamlet – is very out of character and out of sync with the conversation.
Some have theorized that maybe Horatio means Hamlet but Hamlet is not King. He’s a Prince. And if it were about Hamlet, wouldn’t it be “What a King you’d be!”?
I could buy it as an exclamation of praise – the way a friend might call me a queen when I do something with authority.

Their defeat Does by their own insinuation grow:

It rarely works like this.
The toadying suck-ups to authority rarely see consequences beyond their own loss of self respect.

If there were a physical expression of Hamlet’s line here, it would be a big rain cloud of destruction. Every time Rosencrantz or Guildenstern insinuated himself into the corrupt orbit of the king, the cloud would get a little bigger. The destructive storm cloud would hang there over them, sucking up each suck up like an anteater sucking up ants. Soon it would become so full it could do nothing else but rain destruction over them.

They are not near my conscience.

If our conscience were in an actual physical location, it might be easier to recognize when someone was without one. We could run them through the MRI machine, check for the conscience – and if they are without , we don’t let them become politicians or doctors or any job with people’s fates on the line. I mean – there are very few jobs that a conscience-free person SHOULD have. A conscience tends to come in handy in every profession. But – some more than others.

So Rosencrantz and Guildenstern go to’t.

So do we all, eventually. Though hopefully not to an execution the way they are.
I have always been spooked by execution. I used to have nightmares as a teen in which either one or the other of my parents had been condemned to execution for reasons that were not clear. The state, the authorities, the government seemed more powerful than any other means of death I could imagine. More intractable. More – immovable. My protests more desperate – a hope for justice still bumping around in the dark like a moth.
Rosencrantz and Guildenstern don’t endear themselves to many in this play – but the notion of anyone getting executed freaks me out a bit.

Maybe they escaped?

Maybe they were killed by sea pirates instead?

Now, the next day Was our sea-fight.

It would be funny if the sea-fight were not a surprise attack by pirates but an event planned and scheduled into the voyage like shuffleboard games on a cruise ship. Like – Monday is the cabaret.
Tuesday is water sports in the ship’s pool and Wednesday is our sea-fight.
Thursday is Taco Night and Friday is the dance.
I’m picturing it all written on one of those school calendars with cheesy clip art scattered here and there and it makes me laugh. I picture Hamlet drawing pirate hats and swords surrounding Sea Fight Wednesday.
I also want him to really have planned it.