I agree with Rainfeathers here - folks will steal and yes adding tools like this does make it easier.

However I can also see why companies like DA will add tools like this, to ride the the you-tube effect and social networking bandwagons. It's all about business and making money not protecting artists, unless you have a commerical interest in that artist. So you'll see more of it, and image theft, as sites like DA add tools aimed at Bloggers. 

I think it's fair to say that most bloggers are not malcious, they just want a 'pretty picture' on their page. Many folks are unaware of copyright so maybe a gentle educational approach is required by the likes of DA. For example an interstatial page explaining copyright if you try to download a large image.

But if someone is genuinely naughty we'll set Gabe on to them :)
Just kidding there.

Pinky - you left the lens cap of your mind on again.