I'm pretty sure the EU's plan was to lean on NATO and NATO's plan was always to hold out just long enough for the US to roll in with a half dozen carrier groups.

Inherently everyone would know that rods exist on orbit and would destroy them before they reach an orbital position to deploy.

Unlike aiming conventional munitions, on-orbit maneuvering is extremely difficult and would be pretty easy to counter. Every nation that we would need that kind of yield from would be able to shoot the bus carrying the rod which would almost certainly disable the ability to accurately de-orbit it.

Basically, they are easily detectable and way easier to stop than any other weapon of mass destruction.

Sometimes practicality isn't the point of research. A Mars colony isn't about being a better place to live than earth. Moreso, what can we learn about living on Mars that would make life on earth easier. Further, if we ever get to a point where terraforming Mars is even viable on a generational scale you have an ecosystem that you can afford to experiment on instead of damaging your home planet. There's also the point about make humans multi planetary which makes us much more resilient to basically any kind of extinction event.

I really don't think anyone has ever made the point that colonizing Mars will be easy.