It's morally wrong to target scientists in my opinion, but as it's obvious Israel doesn't seek an all out war (it doesn't want to, and hasn't yet targeted military targets in Iran) it's their only shot at stalling the program other than diplomatic rhetoric.

And for what it's worth, I don't think America would throw nukes at Iran would the latter nuke Israel. Perhaps under the previous Administration, but under any other, including the present one, it would simply not do it.