Listen. I like Jack, I do. And I love that Cas loves Jack. But I think a lot of people forget why he loves Jack. Why his purpose became protecting Jack and being Jack’s father. It’s not because it comes naturally to him, or because he made the decision to do it unprompted. He’s an angel, not a father.
In the womb, Jack showed Cas the utopian future he was going to bring into existence. Cas with his wings back, Sam running through a field, and Dean looking at Cas with happiness and saying “thank you”. That’s just what we know he saw. He might have seen more. And that’s what Cas was working for. That’s why he was protecting Jack so vehemently, even at the expense of his friendship with Dean and Sam, even in the face of Jack killing Mary; he thought that if he protected Jack, it would all work out in the end, and that future would come to fruition.
Everyone always thinks the best of Cas as Jack’s father, but he loved Jack and cared so much about Jack because he wanted that future. Jack was his purpose. He wanted what Jack showed him, and was willing to go to any lengths to get it.
AND HE NEVER GOT IT.
Jack lied to him, to get him to protect him, to get him to be the father that he wanted. Jack chose him as his father, not the other way around, and he manipulated him into being what he wanted with visions of the “future”. He showed him what he wanted most, to get him on his side. He truly was Lucifer’s son all along.
Even if the cut scenes of the future from the script weren’t canon, I still think Jack lied. There’s NO WAY Jack showed him the future that actually happened, and Cas was motivated by that. No way. None. Himself being taken by the empty, Dean being killed on a stake by vampires, Sam having a kid he names Dean and dying of old age. Yeah, that sure seems like a purpose to rally behind alright! (that was sarcasm btw)
And I think Cas was still holding out hope for whatever future he did see when he was taken by the empty. I think he still believed in Jack then, and still thought it would all turns out okay. But it didn’t. Because Jack lied to him.
Yes, I think Jack basically taped into Castiel’s desires. Because the three images shown to Cas are exactly what Cas desired. a) Cas with wings/powers again. Season 12 Cas was feeling especially useless, so of course he would want his full powers, but also the wings... I don’t think that was even explored enough how much he missed them (although he said at least once that he did, so yes). b) Dean happy and appreciating Cas. Need I say more? Pretty much on the nose of what Cas wanted from Dean. c) Sam - vague but generic Sam in a good place. Cas wishes Sam well and all that. The other reason I don’t think Jack showed Cas any version of a future is that... Jack never showed any ability to predict the future. Even the most powerful beings (Chuck, Amara, Death, etc) were murky on the exact future, but aside on that, Jack... never had seer-like powers. The question then becomes did Jack show a version of a future that he (Jack) wanted/planned to create? Maybe. What we know of Jack he did want for his family to be happy, so sure, baby Jack could also have generally wanted to create said paradise. I agree 100% that it was still manipulation. It is why it took me SO long to warm up to Jack. Through manipulation, he took away both Cas and Kelly’s freewill. But I also think Cas did grow to love Jack for his own sake, not merely for the “future.” As for the empty, maybe Cas did still have faith in Jack. Which wouldn’t be totally misplace though? Technically, Jack did bring back the world and get Cas out of the empty and the writers might argue that “paradise” is really Heaven after they “fixed” it. (I have all kinds of issues with this interpretation, because the rest is terrible, but still, you can see that the writers were trying for this faux perfect happy ending.). But I agree, it’s faux and most about the ending was terrible.