It's true being underneath the water limits your sight! While our fascination for space has everything to do with the possibility to see landscapes at a great distance.

But an underwater base would still be submitted to Eaeth's gravity which won't be the case on Mars.
To colonize means to settle doesn't it? Taking the family or even founding a family, making children and having perhaps more than 50% of the population not working (either at school, retired, on vacation, etc).
And all of this under 38% of Earth's gravity and either underneath the ground (against UV's) or inside a bubble.

The whole idea of space exploration has to do with our love for freedom, our urge to discover, our willingness to go where no one has goen before, to find new possibilities.
But it also means to be able to return back home.
And this is going to be very difficult to the Martian settlers.
Earth's gravity will seem 2.63 times stronger than what they're accustomed to!! Mars settlers will have limited freedom (far less variety in landscapes compared to Earth, spacesuits everytime they're outside, no trip back to Earth at all time or even at all.
When the Berlin Wall collapsed, the East-Berliners came to west Berlin and discovered the western world. They were extremely happy!!
But at the end of the day, they returned back home.
This is the best expression of freedom.
But then, the grass is greener out there, isn' it?

Raoul