Wasn't the same argument made against going to the moon?
Visiting is trivial compared to independently thriving.
Which reasons, as for 99% of everything else like that humans have ever done, will likely be economic or military. When it makes dollar-sense to do it, we'll go. Not sooner. Not really, and not for the long haul.
I'm doubting we'll do large-scale human colonization of space for a long, long time, if ever. We might do mostly-robotic asteroid mining within the next 100 years, and a couple visits to e.g. Mars might be made, but nothing serious.
On a slightly different tangent, The Moon Is a Harsh Mistress [0] suggests that whosoever sets up the lunar catapult first will likely become "masters of Earth". I think I'm going to start learning Chinese! [1]
[0] https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress
[1] https://spectrum.ieee.org/china-aims-for-a-permanent-moon-ba...
Was the argument wrong? If it was wrong, are the reasons it was wrong applicable to the current situation?
The truth is we're not ready to set up shop on a more hostile planet. We'd need to be able to spend 10x the resources our current total society can afford to properly seed a Mars colony. Any actual attempts made this century will lead to horrific failure. I can't imagine future generations will have a good taste in their mouth about colonizing Mars when they remember what happened to the first colony.
Colonizing Mars an important avenue for the continuing legacy of intelligent life in the universe. It must be taken seriously. Such half-assed attempts that are being discussed by Musk and NASA today only reduce the prospects of humans surviving past Earth. We need to become masters of Earth before we could ever hope to take on a bigger challenge.