There is reason to treat Hamas as an enemy of Israel; thousands of rockets fired at Israeli civilians attest to that.
If you described the threat of rockets from Gaza in terms of lives lost, it would sound much less impressive: Rockets fired from Gaza have killed some 16 people in Israel, going back to 2001. It's difficult to present that as a legitimate rationale for killing more than 3,000 Gazan civilians over the same time period.
If you describe the problem in terms of rockets launched, though, it sounds much more serious. Who wouldn't take extreme action to stop thousands of potentially deadly attacks?
The problem is, if you're going to describe Palestinian attacks on Israel that way, shouldn't you describe Israeli attacks on Gaza the same way? How many bombs and bullets do you have to drop or fire before you kill 3,000 civilians? Surely some enterprising reporter with good sources in the Israeli military could make a credible ballpark estimate of the amount of ordnance used by Israel on Gaza, and then stories discussing the conflict could include a line like, "Israel, which has fired millions of rounds of ammunition into Gaza…." Or however many the total turns out to be.
Until they have that figure, however, perhaps journalists could stick to giving the number of lives lost on each side as a means of conveying the degree of threat each faces.