As I said above, this is even a false dilemma. You can have both increased security and increased usability by including one-time hashes in URLs that log users in.
Yes, that's the right way to do it, but a URL that makes the user auto-login is not the same thing as actually reminding the users of their passwords. And I bet that quite a lot of people prefer getting their password in a mail instead of a weird URL thing and being forced to enter a new password.
Remember that you and me are not the main target group of a service like this.
