Thanks for the excellent question.~ and thanks for bringing this to my attention Cristián.Most of the FB connect plugins work the same way. They authenticate a User through FB, and an account is automatically created for them inside WordPress® with the Default Role, which is "Subscriber". So if you're protecting your content at Level #0, this should work just fine.
If you're protecting content at higher Levels, then those people coming in through Facebook Connect will need to pay for access to the higher Levels, using a PayPal Button/Form, or whichever Payment Gateway you've integrated with s2Member.
All of that being said, it sounds to me like you might have a larger problem here. You mentioned that your Level #1 account was being redirected to the Membership Options Page when attempting to view content protected at Level #0, is that correct? If so, that's definitely not right.
What browser are you using, Safari?Please see this bug report here for some additional detail.
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