It's been in the news lately--Pig gestation crates. The point is to prevent pregnant sows from hurting themselves and others.

The crate debate – your take on gestation stalls – Eatocracy - CNN.com Blogs

So far I've only ever had 1 pig. We didn't breed her. What's left of her is still in the freezer.
But I think if I bred pigs for a living I'd probably be interested in making sure they aren't dangerous to themselves and others. From a business perspective, it's in a farmer's best interest to keep as many of their animals alive and healthy as possible.
It's not realistic to build a private stall for every breeding sow on larger farms, and IMO it seems the crates are a decent alternative.

I definitely do not like massive-scale industrial farming. But banning the use of the crates will hurt smaller farmers too.

I liked these 2 comments in particular.

Why would a farmer purposely harm an animal? Farmers are not monsters that mistreat their livestock. And why would they? Those animals that they raise from birth are their income and help feed their own families; it’s silly to think a farmer would sabotage his own well-being by mistreating animals.

I have a B.S. in agriculture and have studied the process of raising pigs–not to mention the fact I live on a farm and deal with these things every day. I have seen sows fight viciously, it happens, just like women on reality tv! What makes anyone think they know more about farming than the actual farmer and the scientists devoting their research to making farms more efficient? I do not go into my doctors office and demand he change the way he treats me, I understand he knows more.

[Banned-purlyrocker]

If I understand this correctly when the pigs are pregnant farmers put them in crates so they can't fight, hurt themselves or others (thus hurting the offspring).

I crate my dogs, well less so now but when we first got them, we put them in crates. Big enough for them to stand up and for them to turn around, the perfect size. This was because when we first got them they'd run all about and get into things that could make them sick or really hurt them. Once they learned their boundries we could let them out of their crates. I don't really see a difference between crating my dogs and crating the pregnant pigs.

Yes, it'd be lovely if all the animals on the farm could roam around without worry. Like in Charlotte's Web! And if they could burst into song and spiders could spell, why that'd be just swell. But if the pigs are hurting themselves, or the other pigs/aniamls/people, then crating sounds like the best opition to me.

I'd be fine with a mandate that all crates must be X size by X size for pigs of X size to make sure there is room and none of the animals are being mistreated.

This explains crating and farrowing a little better.

Clarified – What are gestation crates? – Eatocracy - CNN.com Blogs

I like your example of Charlotte's Web. I think that and a few other animal stories like Babe and so on have given people an unrealistic expectation of life on a farm. Pigs are destructive and dangerous, unless it's a pet pig you spend a whole lot of time taming.
At the time of butcher a young pig (of the breed I had anyway, a Yorkshire) will be around 300lbs. A sow of breeding age will probably be in excess of 500lbs. I wouldn't want to be in the midst of sows fighting for territory and food.