privacy is the main reason. corporations can not steal/sell your private data if customers are not giving them the private data. giving the data is not necessity with bitcoin.
yeah for me privacy is also really important, besides that i really like to have control over my own money as i dont need to use any banks
And what is the connection of your statement to the thread title?
If customers will use bitcoin in purchasing in some of the big online merchants out there, it's mandatory to give your personal details to them since it's part of taking security and concern for their clients. Even in fiat transactions that is required. If people don't want the idea then don't desire to accept bitcoin by those big merchants.