A collecting discussion: owners unwilling to deal a rare card you need

Yesterday while cruising around the Blowout forums as usual, I caught this thread, which immediately piqued my interest:

It sparked quite a bit of discussion from the board, and rightly so, considering the content.  While much of the thread devolved into the inevitable bunch of childish insults and off-topic crap, there was some pretty good discussion going on, generally siding with my point-of-view.  Mainly, the two sides were:

• Jeez, what a douche!  If you offered him more than he paid for it, he's STUPID not to sell it to you, and by not doing so he has bad karma heading his way.  He totally owes you this card, bro.
• Um, he OWNS the card, and just because you have three of the other four he's obligated to sell his to you regardless of his attachment to it?  You probably screwed yourself by telling him this was the last one you needed anyway, now he's got you by the balls, and if I was him I wouldn't sell it to you because you're the one being a jackass.  Leave him alone and go cry, emo kid.

This made me wonder how the most reasonable group of collectors I've known--those of you that write your own blogs and/or read them--would approach this situation.  So in the interest of spurring some good old-fashioned internet discussion, a few questions:

1. If you were in this collector's shoes, how would you feel about the other guy refusing to sell you the card and telling you not to contact him anymore (based on the little you know contained in this post, to be fair)?
2. If you were the person in possession of that fourth card, how would you handle the guy trying to buy your copy?  Would you sell it to him or no?  Why not?  If you sold it, would you gouge the hell out of him or just go for a tidy profit?
3. Do you think collectors that are (presumably) acquiring a set of something rare like four 1/1 cards are entitled to the remaining cards (at a reasonable price, of course) when they get to a certain point?

Please have at it in the comments or by emailing me.  I'll be happy to update this post highlighting those comments if enough people make them and there's interest in me doing so.  This just seems like an appropriate instance for some actual card collecting discussion!