Then I am very curious to be enlightened as what is not the shallow way to evaluate this issue.

I think an immigrant comes to any foreign land keeping few things in mind like better job, better pay but overall he wants stability. The stability can only be achieved through somekind of permanent setting, somekind of assurance that he won't be kicked out overnight because of lack of some documents. At present the only document that provides that is a green card if u r in US, a PR if u r in Aus, Can or so on.