I don't know why I'm weighing in here, I must be a masochist, but.....
In reference to the OP, yes, the boy deserved to be punished. He was told by the school not to sing that song, and he did. He deliberately broke a school rule, and the requires consequences. However, I don't think the punishment fit the crime. I think the suspension was overkill. The child wasn't doing anything sinister, he was doing what 6 year old boys have done for eons, and will continue to do for eons more, he was annoying a 6 year old girl. He knew the song bothered her, so he sang it. It's the modern day dipping pigtails in the inkwell.
I have a lot of kids, and believe me, they have done worse than shake their fanny and sing to annoy their siblings. Had that been my daughter and she complained I would have told her, "So what? If that boy wants to make a fool out of himself let him. Walk away, the more attention you pay to it and the more he knows it annoys you, the more he will do it." I just don't see it as that big of a deal.
Now onto the rest. Everyone has to raise their children in the method that they see fit. It doesn't make one parent superior or inferior to another and it doesn't mean that one parent's child will turn out better than another. Good and bad have evolved from both overly protective and overly permissive homes. I am not one to censor language much around my kids. Naturally, I try to keep things age appropriate, but if my kids do see or hear something that is not appropriate for them I tell them that they cannot do/say whatever it is and why. So, yes I will tell my 3 year old that "sh!t" is a word that only grown-ups can use (and daddy is a grown-up

) and that they will be in trouble if they use it, but I certainly wouldn't go around telling other parents that they are better or worse parents than I, or that their children will be better or worse people than mine because they feel differently.
My example is this: my friend's daughter is very into cheer leading and has been since elementary school. Her daughter encouraged my daughter to try it and my daughter was interested. We went to one of their competitions. I felt that the outfits were too skimpy, and that the routines were too adult for elementary children. This was my own feelings based on my own beliefs and the personality of my own daughter. I told my friend that we didn't think it was for us. That's it. No judgment on her letting her daughter do it. What was right for her kid wasn't for mine. Her kid still cheers, mine never did. They are equally as well behaved and both get good grades. They have different interests and personalities, but one is not better than the other.
Every generation that comes along bemoans the differences in the younger generation. That has also been happening since the beginning of time. Some things are progress, some things are just change. Yes, my kids hear more overtly naughty language, but on the flip side my daughters are allowed to get an education. My kids see more violence on TV, but my kids can sit anywhere on the bus they want. My kids clothes aren't as modest as the 1800s, but my kids will never work in a mine or sweatshop.
Life is all about ebb and flow and give and take.
...and now for an old school reference: "You take the good, you take the bad, you take them both and there you have the facts of life."