I just watched the 1978 version of Invasion of the Body Snatchers, and I enjoyed it — expect for the romance between the two leads. I thought it was simply a Token Romance that had little to do with the story. But a few hours later, I got it — it was supposed to be like that. When you're under stress like, say, being two of the only people who aren't changed into mindless aliens, of course you're going to jump into something like that. After the movie, had they survived, I would've fully expected them to fall apart. — Otempora
Actually it's implied that the two really like each other from the beginning - there's some Rewatch Bonus to it. They just didn't make any moves on it because Elizabeth was married.
In the 2007 version, the pod people were trying to convince Carol that a world populated with pod people would be a world of peace. A world without war or crime. This is so much a point that Carol and Ben ponder whether or not they should have let the pod people win. But the entire duration of the movie, the protagonists watch the pod people committing acts of violence against people who aren't yet converted.
The pod people explain this - they pretty much figure that the world without war or crime is all set once everyone on the planet is converted. So, if you're immune, you're SOL. It's hypocritical, but the pod people don't see regular people as "one of them".
Since there would be "peace on Earth" but no longer any human race to experience that peace, why is letting them kill off all humans and then no longer having violence at all a tempting prospect?
The 1978 version uses the more advanced special effects of the time to address some of these issues, such as what happens to the original body when the pod opens (withers into dust), and what happens when two...animals sleep next to one pod which has been injured (confusion).
The 1978 version did have its own bit of Fridge Logic, however. The invaders in this version first come down as spores which grow into flowers. The pod people still try to ship big heavy pods all over the place instead of flowers.
It's implied in the opening shots that the spores assimilated the plants they first landed upon when reaching Earth, and then adopted that form into the pods we see later.
The ending of the original film. Yes, Bennell did finally succeed in getting the word out, but can the fighters stay awake for long enough to oust the invaders? Will they start hallucinating or die from sleep loss?