Maybe you're right. He was also left behind after his people had left, so he was pretty ticked off.

The term they used was harvesting though, not kidnapping. Generally, when you harvest something, you kill it and take the parts that you want.

I do not really equate harvesting with killing. The idea of a farmer saying, "I am killing my crops." seems a tad extreme. I prefer to equate it with collecting.

Perhaps they see Earth as this giant farm, with replenishable slave-candidates. They harvest a 'few' humans now and then, let the species repopulate and come back for more.

There's been other spoilers earlier in the thread, but just so you know...
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I enjoy deconstructing movies as much as the next guy, but you have to draw the line somewhere. This was not a movie about an alien invasion. This was a movie about one man's quest for faith. It was about how he lost it, and how he regained it. You have to forgive some of the (big) plot holes dealing with the alien invasion and focus on the point of the story.

That being said, I didn't really believe Gibson's reclamation of faith. I've only seen it once, but I found the whole "faith" part of the movie poorly done. I may be missing something big (which is why I want to see it again) but how exactly did the death of his son make him believe in God? Was it all to do with what his wife said when she died? ("See," and "Swing away?") Not enough for me.

Now don't get me wrong. I really liked the movie. I don't think he'll ever better than Sixth Sense, but Lucas can't top Episode 4 and 5, Rick Moranis can't top Strange Brew, and the Zuckers and Abram's can't top Airplane. But the thing is, even a second rate M. Night Sh(something) film is a lot better than most of the schlock put out these days. The cinematography in Signs was great, as was the directing (camera movement and framing esp.) The acting was very good, especially the children and Joaquin Phoenix. All this and the pacing made for a very tense and exciting movie. I give it a thumbs up, even if it did disappoint in the areas of Alien logic/strategy and main character motivation.

His son did not die. Listen to what he says outside the farm.

[Paraphrased]
"He couldn't breathe in the poison, he couldn't breathe in the poison, etc... ..."
[/Paraphrased]

Things happen for a reason, that was what the movie was trying to say. He thought the his son's asthma attack was unfair, but it turned out to be a blessing in disguise.

Hee, hee... just because I nitpicked on the alien invasion part, does not mean I was not paying attention to the main plot of the movie. ;) I love the movie.