Yes. As I understand it, after talking with Vene a few times about it, the short version is the body is set up to intake 20.9% oxygen from the environment. Free radicals naturally occur as chemistry in the body utilizes oxygen and the body contains "antioxidants" to combat these free radicals that would otherwise harm tissues through the process of "oxidation." The unpaired electron of the superoxide O2- ion (free radical ion of oxygen) essentially steals an electron from what it comes in contact with, which is hopefully an antioxident such as glutathione that would prevent it from binding to tissues and interrupting important biological processes.
When we increase the FiO2 and the body has nowhere to put it, many more free radicals form than naturally would which can deplete the antioxidizing reserves of the body and actually worsen disease processes, lead to new disease or form localized scar tissue.
Oxidation: (yes I linked wikipedia)
http://en.wikipedia.org/wiki/Oxidation
What he said is the short and simple version.
I would just add the free radicals damage cell membranes (particularly RBCs), this damage can initiate apoptosis cascades, attract immune cells from IgM and IgG binding(like fixed macrophages in the spleen), which recognize the damaged cell as foreign, expose compliment binding proteins, and initiate inflammatory cascades.
While this cellular damage may initially be subclinical, it can take days to manifest. Even if it doesn't manifest as acute injury, in can cause damage that will shave years off of both quality of life and total life.
If you think cellular injury is too small to care about, let me put it into perspective...
If you take a mole of oxygen, use 1/2 to deplete natural antioxidants, you will damage 1/2 a mole of tissues.
Those tissues most likely are going to be type I pneumocytes, RBCs, vascular epithelium, zone 3 liver cells, and renal medulary cells.
In infants, to that list, add the retina.