They wouldn't want me. I'm fat, old and falling to bits.
Even during world war 2 you were excused if you were a conscientious objector. You could choose to do civilian service instead. I would imagine the same would be true today.
Also I think it depends what we're fighting for. I think most people would, if it came to it, physically defend themselves against an enemy that came en masse to take over the country and your choice was fight them off or be taken under the rule of that country and you had bombs being dropped on people's houses!
Although that type of war, I really doubt we'll see that again anyway.
But if that did happen and if the armed forces were not large enough in number to fight back then maybe people would want to join in in self protection, or maybe they'd say ok well, it's not worth fighting over so ok, X country now rules us and we'll just do what they tell us to. Who knows?
Oil and other resource grabs disguised as wars can fuck right off though.