Assuming you're in the USA and don't plan to donate your shares to charity...is there some perceived disadvantage to paying LT cap gains taxes today vs paying LT cap gains taxes at some unknown date in the future? Do you think LT cap gains rates in the future won't be the same or higher than they are today?

This is a very good question. Some people are betting on the fact that basis step-up remains in the law for the indeterminate future. So if you have Berkshire (or other) shares that are almost completely comprised of capital gains, when you die, the basis gets stepped up and the capital gains clock restarts from that point.

The second answer is that if someone has highly appreciated [Berkshire] stock and sells it now, they will only have 76.2% of the money to reinvest elsewhere (because 23.8% has to be paid in income tax). And it'll take quite a bit of time for that 76.2% to "catch up" to where the [Berkshire] stock would have been had they simply held on to it.

I have a different discussion that I want to have about capital gains, but I will save that for later in a dedicated thread.