Columbus had a hard time finding anyone to fund his idea of traveling west to seek India until the new monarchs in Spain decided it was cheap enough to risk and he found a whole new land mass (sadly to loot). People have always taken risks and gone to new places and found things not imagined by others. Space will be no different; the only difference is we already know a lot about it. Whether governments or industry or some crackpot does it, it will happen because someone wants to try.

If humanity survives for the next 400 million years, undoubtedly space will be part of our future.

Currently organized human civilization as we know it has a much less than 1% chance of surviving the next 400 years.

I think that the evolution of land animals (and especially humans) has had more negative than positive consequences for sea life.

This analogy makes no sense. The argument stands without the assertion that we certainly will not ever have a future in space.