You're not contributing anything to this thread. It might very well be fruitless to discuss this topic but we're doing it anyway, you are free to leave us alone or make an actual contribution, but you're not stopping the discussion merely by questioning whether it's fruitful to debate. I'm not sure what you think you're adding to this all by doubting the credibility of everyone in this thread without even daring to take a stance yourself.
On the topic of expertise, I will be the first to admit I'm not an expert, but I am against spanking based on cursory research, a lot of experience with abused people, and a general principle that if an action is likely to cause a lot of harm and is never truly necessary, it is better to err on the side of caution and abstain from doing it. I think it's a pretty reasonable position all things considered and if I can convince even one person that spanking your child is bad, that's a job well done in my eyes. That is, I guess, why I like to argue on the subject despite the fact that I, nor a lot of other people in this thread, technically have what you would call "expertise" (on that note, for someone who does not claim to have expertise in the subject yourself, you do like to make a lot of assumptions on where other people get their info from - have you ever taken an intro college course on psychology, or are you simply making assumptions here?)
By the way, I'm not sure if you are insinuating this yourself, but it's worth noting that parenthood does not automatically grant someone authority on the subject of pedagogy. There are too many parents who have bad ideas on parenting in general or are simply too lazy or unstable to be able to raise a child properly.