We change our preferences all the time. So even though your tendency is to be this, this or this, you might wake up one day thinking you want to try something new. If they're customizing the site based on your past behavior, then they've really limited your ability to change and make choices, which is the natural tendency of humans. The positive benefits of personalization are too often neutralized by the objectionable business practices of some vendors. The trend toward this attitude is likely to increase as more companies attempt to exploit the Web as a marketing vehicle.
Customers feel the ongoing siege of unsolicited emails is intrusive and wastes their time.
Invasion of privacy. Customers resent feeling that someone is watching them. It feels like Big Brother all of the time. I mean, nothing is sacred anymore. Limitation of options.