The key part of that rule is this - "a runner's baseline is established when the tag attempt occurs and is a straight line from the runner to the base he is attempting to reach safely". So until the tag attempt occurs there is no established baseline. Until a tag attempt occurs a runner is free to take whatever route they want from base to base. A runner could run out to where the right fielder is standing if he wants - until a tag attempt occurs. At that point the runner is now confined to 3 feet to either side of a straight line from the runner to the base he is attempting to reach safely.

I see what you're saying. But in some sense you could argue that the runner is simply returning to the base in a straight line. On his return path to the base he isn't doing anything out of the ordinary to try and get hit by the throw. It's not any different than a base runner getting hit by a throw in a run down. But I guess you are saying that the act of taking a lead in a straight line to the pitcher is a deliberate act to interfere.

Here is a rules interpretation that I saw that I thought was interesting that got me thinking about this - austinumpires.org/skunkplay.html

Also as for being called out for interfering with the throw from the pitcher wouldn't the umpire have to determine that it was an intentional effort to interfere. If the runner simply turns his back to the pitcher and goes back in to first standing up it's not his fault that the throw hits him. Right? Or are baserunners required to duck or slide to allow a throw to come in?

But I believe that a runner is entitled to make any path they want when running the bases. Essentially a runner defines his "base path" by the path that he takes to the base. Think of a runner that is speeding around the bases trying to get a triple. There are no requirements for him to be in any particular path. He can circle the bases any way that he wants. It's only when a fielder is attempting to tag him that he is now required to stay with the baseline that he established.

See this for more information - austinumpires.org/skunkplay.html

I don't think that is true. Runners are not compelled to stay in any sort of line when they are running the bases and not being chased by a fielder. Think about a runner who is trying for a triple. He is allowed to take as wide of a turn as he wants. He can run as wide as he wants between first and second. And also between second and third. There is no rule that says he must stay within 3 feet of the straight line between bases. That only comes in to play when a runner is being run down by a fielder with the ball trying to make a tag.