“Ballistic and cruise missiles have the same general range in payload.”
I suppose things have improved, but the circular error probability with ballistic missiles has not been generally good. Also, you need to know where the targets are and there has been too much coverage of the subject to believe the Syrians haven’t dispersed and/or spoofed the targets. Also, ballistic missiles tend to set off multiple alarms in neighboring countries and could lead to an accidental engagement. If we provide prior knowledge of a launch to the Russians we’d might as well stay home because the targets won’t be there. (This is all about image and politics. If it were about smacking the hell out of Assad, the only way to do that is with no prior warning. The opportunity of surprise has not only been thrown away, it was shredded first.)
The SCUD CEP is not very good. They’re still pretty much glorified V-2s. You’re correct that it’s likely we would not engage targets in this fashion due to the heads up it provides. If it were to be carried out like that, most likely it would be a secondary strike against fixed, hardened targets. Obviously, Israel has some real concerns about inbound ballistic missiles, wants to be prepared, and wants others to know they are.