Except most of us are creatures perfectly evolved for our environment, to Earth’s gravity, the mixture of air, the pressure at sea level. Change it and a body will suffer. Pack the ship, or space suit with too little oxygen and we suffocate, too much and things catch light.
Oh and humans are a toxic box of gases and disease. Filters and scrubbers have to fight the effect of people and equipment to keep the environment safe. And it’s not just these that are the danger. The Mir space station’s mold problem caused a build up of dangerous gases, making humidity a another fine balance to be sought. Comfortable enough for humans, but not a breeding ground for fungi and mold.
Then there’s the bombardment of the ship and everything in it with radiation. Light could overheat a ship. Galactic cosmic rays will penetrate the ship’s shielding and cause damage to the human body. Astronauts have reported seeing flashes as their crafts were hit and it’s still unknown what long term effect this powerful form of radiation has on a body…
Oh, you don’t want to go? That’s fine. I think, Doctor Who is on.
The TARDIS. Now that’s the way to travel.