I disagree, it is a perfectly viable defense that you need to take care around. It's no different to having a turret or alarm on a motion sensor, or a claymore mine. These are very viable means of defending an area, but they don't discriminate between friend or foe so you use them on approaches that you don't expect to be using yourself, otherwise you approach with extreme caution.

The fact that Valheim introduces anything like an automated defense is already a big stretch. Simply remember the mantra "Face towards enemy".