Legal? Probably not. But there has been little interest for Israels international allies to uphold legal principles when it comes to Israeli actions.

Rational? In order to assess that we would need to know, which information they had when they made the decision. Probably we’ll have historians analyze and discuss this in a few years.

Legitimate? From what we know the strikes were aimed and hit military targets, in particular air bases. Weakening Israels ability to bomb people relentlessly like the continue to do in Gaza and Lebanon will prevent many more civilians being killed in those air raids.

Ultimately the problem with every military escalation is that there is only three possible scenarios. Either one side, or the other side miscalculated their strength and resolve compared to their enemies, or both sides miscalculated. If everyone involved calculated correctly, they wouldn’t bother fighting.