Please anyone elaborate why hydrogen peroxide is not used as an oxidizer for main propulsion. I see that everyone agrees on this but from my point of view its a big flaw. I think that industry has seriously overlooked the potential of this compound and that future of cheep space flights lies in it's use.
HTP has been used as an oxidizer before. Kind of. See BLACK ARROW and the rest of the British keroxide. Turns out HTP by itself isn't a great oxidizer, but when you catalyze its decomposition into water and O2, you get lots of dry steam and hot O2, the latter of which is an excellent oxidizer. In fact, it's so hot, it's basically hypergolic.
But there's major disadvantages.
Even though 95+% peroxide is perplexingly more stable than 35%, it's still got a shelf life of months at best (but recent work seems to be really turning up that number [Source]).
Your Isp is horrible due to all the water in your combustion chamber.
It's not much less toxic than other hypergols. Maybe it won't give you cancer, but you don't want to be breathing in the stuff in any volume much greater than 5%, much less 95%. It'll deeply burn through your skin in seconds.
It's not even that stable, and it likes to explosively decompose things. The longer it sits, the less stable it gets. An HTP torpedo aged, allowed a tiny bit of HTP through one of the cracks, catalyzed on copper, and killed an entire submarine.
Finally, it's notoriously sensitive to any contaminant in the propellant tank. Any scrap of organic material would induce an explosion during fueling.
That said, the biggest reason is simply the lack of research into it compared to other propellants. Initially, the disadvantages were too steep to justify working with it, and while HTP technology has improved, there's still a big knowledge gap between it and the comparatively predictable, well-behaved (if cancerous) IRFNA + MMA/Hydrazine/UDMH combinations.
Do go read that Ignition! chapter mentioned in the comments.
EDIT: I've looked into hydro-oxide engines before (HTP & LH2) and they are generally absolutely terrible. You gain all the disadvantages of hydrolox (massive LH2 tanks, big temperature difference between between fuel and oxidiser) and none of the advantages of its stellar ISP.