There was no demilitarization agreement between Israel and Egypt or peace treaty. There was simply a General Assembly resolution. Technically, the two countries remained in a state of low intensity war since 1948. I'd say, no casus belli is required when an enemy you're already at war with moves a large force up to your border. Though, the reasons are as you say, I'd also add that there was the issue of Israel not being able to financially maintain indefinitely the full mobilization required to counter the Egyptian move.They broke the peace treaty that was signed stating that the Sinai be demilitarised and kicked out the UN forces stationed there.
While I of course agree that Syria was the aggressor in the 1967 conflict, the two countries had likewise already been in a state of low intensity war. A war that began when the Syrians used what was essentially a civil war within the mandate as a pretext to invade, in the belief that they could annex some territory for themselves.
And others will argue, "Israel had no right to..."Thing is, Russia had no right to conduct a referendum in a foreign country.
The precedent just makes the argument more complicated, and opens it up to this sort of back and forth. Although, I don't think it will actually result in tangible changes to the way countries act, only in the way they justify themselves.