Circle to land procedures are quite safe so long as crews are trained and practiced to do same and know the limitations etc.
However, I think that maybe the question we should be asking is, given the area navigation capabilities of most modern aircraft. why is it ever necessary to carry out a circle to land procedure (ok yes there may be certain locations where a straight in isn't feasable due terrain etc)?
A much more concerted effort should be made to approve and regulate approaches which would avoid having to do a circle to land.