I'm afraid the reality is likely to be that once the doors are blown open, electorates will vote for people that will man them with machine guns
Have you got any concrete examples? The temperature range for human habitability is pretty wide; the temperature regularly gets up to 50 degrees in summer in the Gulf States (like UAE and Saudi) yet the quality of life there is quite high, in spite of it being a literal desert. Most of the refugees entering Europe are fleeing good ol' fashioned wars, not environmental catastrophes.
why do you think this? it's next to impossible to completely stop piecemeal border crossings. but beyond a certain scale, it becomes something that militaries can oppose directly. are you suggesting the europeans would not have the stomach for military action against migrants, or that the migrants would somehow defeat them in sheer numbers? if it's the former, I would point out that were are already seeing questionable events with migrant ships in the mediterranean.
Take France for instance, 10% of people living in France in 2021 were immigrants (born in another country). Net Migration is in the 100-200k range per year.
https://www.lemonde.fr/en/france/article/2023/03/30/one-in-1...
https://www.statista.com/statistics/686137/net-migration-fra...
Of course there are people just looking for better economic opportunities, and people who target specific Western countries to be a refugee in (e.g. Pakistanis that show up in Germany - if they were really fleeing from a critical situation they would stop in the first place that is calm and safe, not continue the journey to a richer country), but they aren't really refugees in the actual sense of the word.
I don't know where does this argument come from.
I think it's much harder to get to USA.
An immigrant who finds themselves in New York City, to contrast, will see that the city provides government assistance in dozens of languages and proof of address and things of that nature aren't even required.
Smaller countries this is not the case. For example in nordic countries you can get by quite fine with English.
The hard situation is "a person with knowledge X moving to country Y and applying for work", when they have to apply for work no different than locals yet the work visa requirement attached to the resume turns employers away because it's a damn hassle.
You simply can't grasp that from the employer side