You should maybe read some articles about modern situations where people dodged conscription before assuming what is practical today. The average person who hasn't thought about it for a week is certainly in trouble but..
Yes, fight in advance to prevent such a situation, but don’t assume you will win. It’s good to have a backup plan.
Conscription has never been popular, and I think today in healthy industrialised nations it would be an exceptionally hard sell. Ukraine, Russia and (somewhat) Israel give us hints here of what might happen if the US or Germany or India started drafting all able-bodied young men.
It would be a disaster, but my guess is that it wouldn't stop governments from trying.