You cannot use this as-is for justification for such a conflict.
Compare rocket size with the size of a mountain.
Now take earth's mountain ridges.
Clearly we could lose a mountain, of which many rockets could be made. (Gross oversimplification, but clearly in raw tonnes of material, this is not a problem).
But let's say you DO want this as a concept.
There's a movie that has in Earth-orbit colony and a kind-of conflict between Earth and the Colony. That movie is Elysium. Basically, people ruined earth, and now the rich live on the colony, whilst the poor slave away on earth.
If you place your colonies further away, you could argue that there is a resource (resource X) that allows fast rockets. Resource X is troublesome to excavate, polluting, rare, expensive... you name it. Imagine resource X to be of nuclear origin, but 10x all its factors and you get something that's pretty nasty.
You still need an opponent, though. If me donating you goods costs me a lot, I might just stop. What's preventing me from stopping with sending you goods? Death of a colony? Then why are the people angry? Surely they understand?
The idea is workable, but you need another source of conflict. Ecological conflict on a small scale is usually people not wanting to pay for getting rid of their trash properly, so they just dump it.
Maybe there's one continent responsible for the colonies and it's polluting the world with the constant rocket launches using Resource X. Background radiation levels are on the rise.
Radiation chart: (For better viewing, I recommend the original on XKCD)
Basically, the "daily dose" of 10 micro Sv is already increased to 50 micro Sv, and in the future it looks like it will go up to 100 micro Sv and 250 micro Sv. Now, this doesn't seem bad, but the radiation gets in the food, and the water, and slowly the whole world is poisoned.
Radiation is a scary thing, but it's just one example you could use. I don't think scarcity of resources will work out, unless you create some mystery "Resource X" that is A) Scarce and B) needed.
Iridium would do nicely if you want to use existing resources. Wikipedia lists Iridium consumption as 10 tonnes in 2010. That's not a whole lot, and if the rockets or the supplies needed it, you'd find Earth significantly lacking it.
But again, you run into the issues
- Why do the rockets need it?
- Why does Earth need it?
- Why do the colonies need it?
- And why would the people on Earth be upset if it's used/in low supply, enough to cause a conflict?
It can be done, but I feel you'll have to rely on some other, bigger threat (such as radiation).