Ronaldo to ManU won't end well. Arguments "for" are the same that were used for Ibra's transfer. Sure enough, Ronaldo is miles better than Ibra, but he won't come for free unlike Ibra. He will still be a very expensive purchase, especially if you also consider his wages.
Clubs should realize that not every top team have a Ronaldo. ManU fans keep moaning about lack of balance in their squad etc., transferring Ibra and Ronaldo does nothing to help, in fact, it makes things worse.