No, the main thing is that self-sustaining enterprises aren't up for public debate, so there's no reason anyone would criticize them as frivolous. Whereas anything that needs public funding, like space travel historically has, is automatically subject to a debate about its worthiness.
Sure there is - I know people who would call those things frivolous. Football consumes a serious outlay of energy for comparatively little lasting benefit. It's not scrutinized as often as things that are funded with taxes, but that doesn't save it from frivolity. Anyway, we're probably arguing past each other. I see taxpayer funded science of all sorts as being more worthy than most things, because I view scientific discovery as the foundation of the country's economic competitiveness. Most things seem frivolous by comparison.
