On my current play-through, I avoided the whole mess like this:
1. Went to Sanctuary, spoke with Codsworth, looted the town.
2. Walked to Red Rocket. Met the dog, and banished him to Sanctuary.
3. Built Red Rocket into my personal fortress of solitude.
4. Gained roughly 4 or 5 levels just building.
5. Built up Sanctuary a bit, in anticipation of sending the Concord knuckleheads there. Beds, power, etc.
6. Went to Concord, spoke with Preston, grabbed the power armor, and vanquished the big ugly.
7. Spoke with Preston, and Momma Murphy, and waited until everyone agreed to go to Sanctuary.
8. Agreed to nothing. Didn't volunteer to join the Minutemen, or become the general. I backed away.
9. Waited until I received the "Meet / Speak to Preston in Sanctuary" quest. (this is the quest you must not complete).
10. Never spoke to him again. This is the critical thing.
11. Planted Mutt Fruit, Tatos, and corn in sanctuary, for my personal use *Vegetable Starch / Adhesive). The citizens tend those crops without me assigning them. It keeps Marcy busy.
12. Dropped a water purifier in the river at Sanctuary. Water accumulated in the workbench, and it's a lovely cash crop.
12. Ensured that the defensive value of the town exceeded the food + water production.
13. Avoided talking to Preston and everyone else there.
14. Went and encountered Trashcan Carla, so that she'd start making her rounds. Now I see her at
Sanctuary, and often on the streets between Red Rocket and Sanctuary.
That's it.
Other information you might find useful:
1. Each settlement you encounter will have a quest that unlocks it for you.
2. If you don't complete that quest, then you won't be responsible for the location.
3. If you complete the quest by accident, (some locations have stealth quests),
then don't turn it in.
4. If you do turn it in, and the settlement comes under your care, then remember that these settlers
are invincible. Ignore them.
5. Don't use the workstations in the settlements you discover. You can wait until you arrive home. I could
be incorrect, but I believe that using a workstation could unlock the settlement in some cases.
Alternately, do all the above, but then pick one settlement as your own, (not Sanctuary), and make it your base.
Enjoy.