I'd like to have a word with the intelligent designer, if I may?

In particular, I'd like to discuss oxygen. It's a corrosive agent, as you can see when ferrous metal is left out in the elements. But somehow, it's the one gas in this planet's atmosphere then all animals need in order to survive. Mind you, when you inhale it, it's doing a tiny bit of damage to all the cells it comes into contact with, and the cumulative damage is what we innocently write off as the ravages of old age.

Please explain to me what kind of intelligent designer would do that.