Is infinite scrolling justifiable?

Recently I've noticed a new trend in user interfaces. Facebook and Twitter do this, and I've come across it on other random, less famous sites. However, to keep things simple, I'll just use Facebook as an example.

When you first log into Facebook, you are presented with a "News Feed" that has a certain amount of posts from your friends. The feed extends down past the bottom of the viewport.

Then, when you scroll down, to see the feeds "below the fold", at some point as you move downward, it loads in more items. Apparently, this is called "infinite scrolling".

On my computer, this often causes my position in the feed to jump while I'm in the action of scrolling, which is really annoying.

What's particularly egregious about this UI concept is that there is footer information at the bottom of the page. I advertise on Facebook, and use the link at the bottom of the page to get to the advertisement management interface.

Because of this incremental load feature I'm describing, I often scroll down to the bottom to get to the link I want, when I reach the bottom of the page, it will suddenly load in new data, pushing the footer down again, and I have to scroll down again.

This whole thing seems completely pointless to me. What's the upside? A Facebook page is near a megabyte of data, so saving the few extra kilobytes of feed data for when the user scrolls down is just not worth it.

What's wrong with a link that just says "show more"?

Since this additional data retrieval thing seems to happen as soon as I start scrolling even a little anyway, why not just load that data in the first place?

To me this minor annoyance reeks of some engineers concept of a "neat trick" that does not have any actual appreciable upside.

Or am I wrong about that? Is there an advantage that I'm not seeing? Am I the only one who thinks it's stupid? Do some people like it?