Would a graduate school look down on someone if it took them an extra year or half year to graduate, assuming they still had good grades, research experience etc.
Nope. Going longer than 4 years is pretty common.
Consider that, in another thread, you expressed interest in getting into academic research. This will ultimately require a PhD. After your BS, getting a PhD is usually another 4 to 7 years of school. I would avoid, if possible, adding too many extra semesters onto your BS, if possible, even though it will not affect your admissions prospects for graduate programs.