The logic behind the keep-right law is this:

1. It is illegal and dangerous to overtake on the right.
2. It optimizes the capacity of the road. If you are in the middle lane with nobody to the right of you, the space to the right of you can't be used by anyone, because of point 1.

To address some of your points:

be in the way of people trying to get on

The onus is on the people who are trying to get on to merge properly. Moving over for people who are merging is generally discouraged. Personally, I only do it for slower traffic (large trucks) or with short, difficult on-ramps.

in, what, 4 seconds

The way keep-right is policed is that you are only expected to move back to the right lane if that lane is free for a reasonable distance. Police typically use a margin of 20-30 seconds or so of middle lane camping without passing anyone before ticketing you.

I’m going to merge when it’s -safe- to do so

As you always should. Keep right doesn't change that.

I could technically squeeze in between two of the cars in the column I’m passing

See above. You are never expected to squeeze in between two cars. As long as you are passing you are allowed to be in a lane to the left of the traffic you are passing. The faster driver coming up behind you just needs to wait until you have finished your pass and have the space to move over.

Anyway, my point still stands. You may prefer your keep-your-lane logic over keep-right logic, but in large parts of the world it is against the law, and you should try to follow the laws of where you are. I'm not saying keep-your-lane logic is indefensible when considered in a vacuum, I'm saying you're not in a vacuum so you should be predictable and follow the same rules as everyone else.