It depends on how you feel about the player.
If it was Andrew Luck, you trade two firsts and a second for him all day long. There is not much of an argument to be made that you shouldn't, when your starter is 34 years old, has only won 1 playoff game, and your team is flirting with a rebuild.
If it's Sam Bradford or Matt Stafford, that's a little different. You have to do your homework and make sure that you are sure he's gonna work out. That's why there are workouts, film breakdown, interviews, etc.
There certainly are QBs I would have paid to move up for to that extent, even ones who don't go first overall. I would have loved to move up for a Ben Roethlisberger, who I loved, or also a Matt Leinart, who did not pan out. I would use as an example also a guy like Matt Ryan who had a fairly safe label on him, though lacking upside, as someone who would probably be worth the price.
Manziel might be a little risky. But if the team evaluated him and decided he was worth it, I would applaud the move. Cause you are gonna have to get in the top 5 for him most likely.
If he falls to 10 or something, it's a no brainer.