These are debatable statements at best and naïve at worst. If BNSF defaults on its debt, Berkshire will take a large reputational hit. I cannot prove it, but I am sure the interest rate that BNSF gets has some discount due to Berkshire ownership.
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If you buy shares of Hershey, you are absolutely on the hook for its debt. If Hershey defaults, then the creditors can put it in bankruptcy and recover the money from your equity. Not the $187 that you paid but the book value of Hershey, which will affect the stock price.

Sorry, no, you've entirely missed the point.

My account holds one share of Hershey at $187, and $100 in cash. Hershey has its own debts of $37 per share. Nothing, NOTHING, that happens at Hershey with its debt will allow those creditors to get any of my $100 in cash. I am not in the situation that $37 of my cash is at risk because Hershey has its own borrowings, and never can be as a result of owning that Hershey share. You are 100% wrong in saying that I am "absolutely on the hook for its debt".

By exact analogy, a default at BNSF does not give the creditors of BNSF the right to a claim on any of Berkshire's cash. That's what "non recourse debt" means. Some people think that US law should not work that way, but it does work that way. It is one of the key tenets underpinning the entire bank holding company and utility holding company model.

You point out quite rightly that something big and bad happening at BNSF would be bad for Berkshire and its reputation. But...well, that's pretty obvious, and a pretty different question. The creditors do not have the right to claim Berkshire's cash pile, which is the original point.

Jim