CC totally warps your view. You can read a thread of someone barely getting by and feel that you are quite comfortable financially. Click another link and you feel poverty stricken when you see what others are paying fully out of pocket for two kids at top LACS with no real concerns or worries. Land somewhere else and you believe you have found your brethren, the hard working middle to upper middle class. As many others have said, it is all relative.
In general, I would say that on CC middle class would be those able to afford their state universities without FA except for perhaps the very base level (5k-7k per year) student loan …but not able to pay for a private institutions without grants or scholarships and not willing/wanting their kids or themselves to take out massive loans to do so.