Why to disclose username/passwords?

I have read the FAQs but still do not understand why poken requires my username and password e.g. for facebook. facebook and other social networks offer better ways to authenticate directly on the external site (see: http://developers.facebook.com/connec...)

In any case I would very much prefer to add my personal data and network IDs manually to a poken identity. I do not so much care about the case you use as an argument: If someone else uses e.g. my facebook id to put on his/her poken it is their fault and their problem, not mine. Someone could also give fake printed cards with my name (and my facebook id) away without my knowledge. This is easier for me to deal with than to give usernames/password (i.e. total control over my accounts) to some third party like Poken. So where is the additional value of requiring username/password? I dont think it makes things easier but only keeps many people like me (call me paranoid about web security) away from using poken.

With the present solution I would need to change all my socialnetworks passwords immediately after adding them to poken or just not use poken (which is what I am doing right now). This is sad, since the basic idea is - as already mentioned - really nice.