The only reason I could see builder mode being necessary is the first time you join and you don't have a base. Once you have built a base, if being killed is that big of a problem:
1. build inside so you dont get easily attacked and
2. place a checkpoint so you can respawn right there.
It can be annoying to be attacked in the middle of something but also incredibly fun to go grab some guns and hunt them down.
Edit: It is also FORTWARS. So once you have a base you're technically at war with everyone. But before you have a base... well you need time to build a semi-decent one imho.