Martian Toxicity

[Rynn]

I think people often forget just how insanely huge of a task terraforming would be. Managing a tiny percentage reduction of carbon in earths atmosphere is a hugely costly endeavour, let alone drastically altering the atmosphere of Mars and transplanting a sustainable biosphere.

Point being if you approach the level of technological sophistication and economic size that terraforming is a possibility for you you'll be able to deal with toxic soil deposits.