Adlai Stevenson's suggestion

Yes you are correct. While it seems nonsensical in hindsight, you have to understand the context within which that option was being considered, and how much had changed by the time they were ready to make that deal.

Kennedy always had to deal w/his father's decision to support the appeasement of Hitler before WWII (a decision that JFK was against even then as a young man). Add to this the tension that had built up due to the disaster of the Bay of Pigs (which was largely planned during Eisenhower's administration but falls on JFK's shoulders for blindly going along with the plan).

So at the beginning of the Crisis, it's essentially an option no one even wants to entertain because: 1) it could/would set a precedent for how the Soviets/other nations could threaten/pressure the US into reaching favorable agreements 2) they all realize it is political suicide. As JFK states in the film soon after, this is what makes Stevenson "brave" for even suggesting the option.

However, by the last days of the Crisis, the threat of a nuclear war was so real that it became more acceptable, although still risky. There is an important distinction, however, between what Stevenson proposed and what ended up happening. Stevenson's deal would have been carried out immediately, whereas the final proposal called for the missiles to be removed at a later date. Now this seems like it would be easily identifiable (and someone notes that it's "transparent" in the film), but it does make a difference in terms of public perception/attention span, etc. RFK illustrates the point further near the end when he is negotiating w/Ambassador Dobrynin ("...the United States cannot agree to such terms under threat".)

Hope this helps.

"I have to think hard to name an interesting man who does not drink." - Richard Burton