I'd like to see the actual research article. But they do state spanking in the absence of abuse, which to me indicates a spanking, not something strong enough to be a true hit, though many parents spank pretty darn hard.
Frankly, I don't think it would make much difference if there were definitive research stating higher rates of anything from mental illness to antisocial behavior to suicide in children who were spanked, people would still spank. At it's root it appears to me to be a very obvious way of enforcing your power over another person, and many mainstream parenting theories seem to lean toward showing your children 'who is in charge' and demanding appropriate behavior. Not saying that's necessarily good or bad, just saying. Though I don't personally endorse spanking, I have done it. It seems the least effective method to use on my children for long term change, but it is pretty effective at getting their attention for the short term.
I don't think the argument 'we were all spanked and we're fine' holds any water. Many people also grew up without carseats, without vaccinations, without education, etc., and of course the ones we talked to 'survived'. The ones who didn't survive intact aren't around to talk about it. Just because something was done in the past doesn't necessarily mean it should continue.