on one hand it is understandable that people like Warren Buffet don't understand bitcoin and don't see it as an investment. being old ancient apart, he considered companies that are giving some product or service as investment not a currency. so he probably sees Forex the same way too.
on the other hand calling it things such as "rat poison" and saying "it won't end well" is just silly because we all know that bitcoin is the best technology that could have happen in economy field and also we can see that all around the world people and the government are adopting it with open arms.
If you're even more unforgiving as I can sometimes be when it comes to guys and their sweeping statements like these, you might even say that these dinosaurs know precisely what Bitcoin is, and have always understood its ideals and its overarching potentials. Which is why they fear it and can sense that their end is nigh - even if they won't live to see it, the natural instinct for their empire to thrive long after they've gone will require them to attack Bitcoin as they should, for the threat it poses to their very way of life.
They want history to see them as the champions they've begun to believe they are, and don't want to be remembered as part of a failed institution that consistently brings countries and lives to ruin.