The problems with selflessness

I've read through The Merchant of Venice act IV, and I wonder why the play continues at all. After Shylock speaks “I am content,” to me the climax of the play, it seems most of the loose ends of the play have been tied. One remains, however. It's where Bassanio gives away his wedding ring to a disguised Portia to give thanks for her (him) helping save Antonio's life. To me, it seems we're finally seeing some more character flaws among the men of Venice. Sure, they are selfless, but they are rediculously selfless, to the point where this type of nature will get them into serious trouble. Scene 4.1 after Shylock and the Duke exit illustrates this very well. On line 411, we have the disguised Portia saying “He is well paid that is well satisfied, / And I, delivering you, am satisfied, / And therein do account myself well paid.” Basically, Portia, as Balthasar, says that she's happy to help and that Bassanio and Antonio don't owe her anything. Bassanio basically demands that Portia take an item as payment. “Dear sir, of force I must attempt you further. / Take some remembrance of us as a tribute, / Not as fee. Grant me two things, I pray you: / Not to deny me, and to pardon me.” So, Portia agrees. She takes Antonio's gloves, a trivial item, and wants the ring she gave to Bassanio. Bassanio says she can't have it, because his wife told him he can't part with it. Portia, reasons with Bassanio: “An if your wife be not a madwoman, / And know how well I have deserved this ring, / She would not hold out enemy for ever / For giving it to me. Well, peace be with you.” So, it sounds here that Portia really wouldn't mind after all if Bassanio gives away the ring. After Portia leaves, Antonio reasons with Bassanio: “My lord Bassanio, let him have the ring. / Let his deservings and my love withal / Be valued 'gainst your wife's commandëment.” Bro before hoes, essentially. After this exchange, Bassanio gives the ring to Graziano, who catches up with Portia in a different scene. In an aside to Nerissa, Portia says “I warrant we shall have old swearing / That they did give the rings away to men. / But we'll outface them, and outswear them too.” It seems here that Portia wants to admonish or humiliate Bassanio for giving away his ring, thus making he and his circle of friend's everlasting love and charity. Luckily for Bassanio, though, this was Portia in disguise, otherwise he would've destroyed his marriage. This puts a new spin on previous events in the play. It makes Antonio's deal with Shylock look not like a safe bet gone terribly wrong, but a self-endangering act, all for love for his friends. In this way, Shakespeare seems to be mocking aspects of the Christian faith, as these characters commit selfless acts to the very extreme.