Fanatics - motivated by extreme religious views or extreme political ideologies - are all too likely to engage in atrocities. When they do so, as in the terror attack on Nice, it is not just a run of bad luck, or a misunderstanding among essentially good-willed people. It's not even the fatalistic unfolding of consequences from some moral failing. It's nothing like any of that.
Thus, there's something very misleading about calling such events "tragedies" or "tragic". They are premeditated and willed acts that are better labeled as what they are, as "atrocities", made more particular if we can specify the extreme worldview that motivated a particular set of actions. Thus, we can talk accurately about Nazi atrocities, Stalinist atrocities, Jihadist atrocities, and so on. When it appears that a politician (or a journalist, or whoever) is deliberately avoiding accurate labeling, it looks sanctimonious and even indecent. I can understand taking time before being certain of the motivation of a particular attacker, as mistakes are sometimes made in a rush to judgment. But premeditated, atrocious, murderous, terroristic acts are just that, irrespective of what the more specific motivation turns out to be. To call them "tragic" or "tragedies" is an evasion. Please stop using that wording.