While the cultural effect might indeed be quite important, I really don't agree that it is by far the most important decision. E.g. from a performance perspect

While the cultural effect might indeed be quite important, I really don't agree that it is by far the most important decision. E.g. from a performance perspective, the design of you program is orders of magnitude more important than the language itself. Also, not every platform is as limiting - you could for example start a clojure project, and extend it in java without any fuss.