If it's coasting along it's significantly increasing transit time and thus available window to consider and prepare counter-measures.
> it's in principle quite possible to turn it and fire bombs in the direction of any interceptor
Sure but that means less payload to deliver and even more time for the target to prepare counter-measures.
> and the thick pusher plate makes it actually pretty durable from some aspects.
No matter how thick your pusher plates are they're not going to stand up to the kind of kinetic impact involved.
Sorry, I didn't understand why you were talking about bothering to do that and then crashing it into the atmosphere.
If you want to argue that crashing into the atmosphere would be an inevitable result of the trip, okay, but I don't understand what else it would have to do with my initial comment.
That's not what I'm arguing FFS, I'm saying that'd be the result of going with the fastest possible trip, which would still leave the target significant time to set up countermeasures.
Here's the rest of the paragraph of my original answer since you apparently stopped at the first period:
> If you want to actually deliver your payload in a useful manner you'll need twice that at the very least. 2+ months is a long lead time, and the engine you'll need will make the craft impossible to miss.
The point is that no matter how you slice it, "the difference between building on Mars and building it in orbit" is the target gets a warning several months in advance in the former case, a few minutes or seconds in the latter. One gives ample opportunity to set up and deploy countermeasures, the other not so much.
[deleted some pointless back and forth]
Er… yes?
> Sure, you can try to take it out during the journey, but that may be complicated by it being the highest g ship in existence for the Mars-Earth distance.
That's not really a complication, it's still taking months to make the trip, and while it might be "the highest g ship in existence" that's linear acceleration, it's not a nimble ship performing a tailside in space to avoid projectiles.
> Once/if it arrives, you have the same strategic problems you have if you build it in orbit.
With the pretty damn big difference that you've had several months head start knowing the think was incoming at high speed instead of it just dropping of your head more or less instantly.