1. I am not arguing that our evolutionary past should dictate where we explore. Rather, I'm arguing it must inform how we explore. Space travel is so lethal for our species that we are better off engineering machines, robots or beings that are specialized to operate in space.
2. The energy expenditure, economic cost and sheer distance of space exploration is many orders of magnitude beyond the costs of land, sea or air travel. Comparing terrestrial forms of travel to space exploration is disingenuous.
3. No endpoint. When the great explorers were trailblazing across the oceans there was a reasonable expectation of finding a suitable endpoint with fresh water, edible plants & animals, other people (!) and exploitable resources. With space exploration none of these things are present. We have to carry a suitable endpoint with us during the journey and plant it where ever we happen to land.
Expanding on that last point - imagine a specialized mars robotic explorer that goes on a one-way mission, taps in a sub-surface source of water, erects a basic greenhouse structure, goes into sleep mode for a few months, wakes up, plants some seeds, sleeps a while longer, etc. - it bootstraps a suitable endpoint for human explorers to inhabit years, decades or centuries later.