“When Hamas does it, it’s terrorism. When Hezbollah does it, it’s terrorism,” said Tod Robberson in The Dallas Morning News. So, presumably, it was also an act of terrorism last week when two men on a motorcycle raced through morning rush-hour traffic in the streets of Tehran and stuck a magnetic bomb to a car carrying Mostafa Ahmadi Roshan, deputy director of Iran’s Natanz uranium-enrichment plant. Roshan, 32, was killed, along with his bodyguard, becoming the fifth Iranian nuclear scientist to die a violent, mysterious death in recent years. No one doubts that Israel’s Mossad is behind these sophisticated assassinations, probably with U.S. help. If that’s true, said Andrew Sullivan in TheDailyBeast.com, Americans have “lost their moral compass.’’ We have a right to apply international pressure to stop Iran’s nuclear program, but not to murder civilian scientists by blowing up cars on city streets. Yet some Americans are applauding these murders, including presidential candidate Rick Santorum, who called Roshan’s death “a wonderful thing.’’ Are we becoming the barbarians we’re fighting?

For the record, said David Frum, also in TheDailyBeast.com, the U.S. and Israel have both denied involvement in Roshan’s assassination. But even if this was the work of the Israelis, what choice do they have? There is no longer any doubt that Iran is seeking nuclear weapons, and President Mahmoud Ahmadinejad has been helpfully candid about his desire to bring about “the annihilation of the Zionist regime.” Roshan was no innocent civilian; he was “actively engaged in developing instrumentalities for genocide.” In order to act, must Israel wait until Iran’s bomb is ready—or is used? Would it really be morally preferable for Israel to use its own nuclear weapons “to visit retaliation upon tens of millions of Iranians after a genocide, than to act decisively now to halt it?”

This “abhorrent killing” will not stop Iran’s pursuit of nuclear weapons, said Ali Vaez and Charles Ferguson in TheAtlantic.com. Iran has dozens of scientists working on various aspects of its nuclear operation; Roshan is “replaceable.’’ The assassination will serve only to rally the Iranian public behind the regime and the nuclear program, and further deepen “the siege mentality’’ among the ruling clerics. Indeed, such brazen attacks on Iranian soil may persuade the mullahs to “double down on acquiring nuclear weapons.” And “what if the Iranians start killing scientists” in retaliation? said Avner Cohen in Haaretz.com. Will we still celebrate the death of Roshan and his colleagues if Iran’s terrorist proxies start blowing up physicists on the streets of Tel Aviv or Washington?

There are no good options here, said The Jerusalem Post in an editorial. Diplomatic pressure alone hasn’t worked, and neither have economic sanctions. While “covert actions,” including targeted killings and cyberattacks, certainly carry a risk of blowback and retaliation, they may ultimately help convince Tehran that the West is deadly serious about not letting Iran get nuclear weapons. The morality of this isn’t complicated, said Jonathan Tobin in CommentaryMagazine.com. Iran is a rogue state that has sponsored deadly terrorist acts against the U.S. and Israel for years. Now it’s seeking a nuclear weapon capable of killing hundreds of thousands of people. Given the high price of a full-blown war with Iran, the targeted killings of scientists like Roshan may be “the least destructive option open to either the U.S. or Israel.”