1. It wasn’t that big. The ones in New York and Jerusalem have been much bigger. It seemed like a “me too” demonstration.
2. It’s just “spring training” – the real season begins in a few weeks when (and if) they attempt to conscript yeshiva students (perhaps a better analogy would be to “July 1914” when everything was positioning for war, but war hadn’t broken out yet). I suspect most people expect a compromise (e.g. conscientious objection or psychological unfitness profiles for those who refuse to serve, economic incentives for those who choose to enlist).
3. If they attempt to conscript anti-zionists (i.e. those who hold that a Jewish state at this time is contrary to halacha, and who with a staight face can say they would prefer to live in Islamic Palestine rather than Zionist Israel), they will be able to generate serious publicity that will be exploited by Israel’s enemies (though also, the publicity for a frum peace movement creates many opportunities for kiruv, since many secular Jews identify Torah with militarism and will be impressed to see a very frum peace movement).