So, because there were problems in Europe, there should not have been colonists in the Americas?

Some of those problems were direct in causing the emigration. Religious intolerance. If privation was the only driver, then they found more privation in America. Many colonies failed. Death ensued.
And Scotland tried it, bet the farm(s) on it, which bankrupted a lot of people, and precipitated Union.
And America (I am told) has acceptable atmosphere. ;-)

The proverb about giving a starving man in the desert seems to be apt. (other genders are available)

It is not that it couldn't be done, given enough time and effort (and money let it not be forgotten). It is not that a few deaths would stop the project. But Mars has no immediate resources. All would have to be taken. Or machines to manufacture them. Water? at the poles, where the temperature is - er - colder than any part of America.

When the global warming becomes so pressing that we have to deal with it, which takes money. Mars will not be so appealing in that climate (whatever we have by then)...... Mars is not a back-up system for Earth.

Nero seems to spring to mind..................