Mostly because
Israel says by not doing so, we're saying it's ok.
And maybe Bush does think it's ok that Israel is bombarding Hezbollah and killing what ever civilians (or
UN troops) happen to be in the way. Why would he?
Because Hezbollah is a "terrorist" group. Meaning what? It had been acting previously to oust what it (and the rest of the world, as I recall) an occupying force through what means it had. I don't like their methods, but something tells me if Canadian troops were occupying a section of Montana, we wouldn't be calling the militiamen doing drive-by shootings from the pickups terrorists, even if they did lob some bombs a bit indiscriminately.
Life isn't as black and white as we'd like, it would seem. I just wish our leaders understood that.