If you live in the right area, being “bunkered in” with the right equipment, supplies, and a decent neighbor-network, is exactly the right thing to do.
I live in a sparsely populated area with several like-minded neighbors. When the SHTF, a couple of large black-powder charges can drop bridges making our area extremely difficult to access.
A mech infantry battalion MIGHT be able to dislodge us, but nothing short of that will be able to even hurt us much.
I live just outside a small town. Our subdivision and town have a history of helping each other during emergencies. My block has had a lot of new people move in though that we don’t know that well.
Now that you mention it, we could probably prevent traffic from the big city, but then that would also destroy the ability to transport supplies especially medical supplies.