Is the prohibition against leaving the Land, generally speaking, still in force today? After all, the Land was fairly empty of Jews throughout the last two thousand years, and even today, when there is a Jewish state in the Land of Israel, there are millions of religious and Haredi Jews who continue to live abroad, and some even claim that it is forbidden to live in the Land of Israel before the coming of the Messiah. Does it make sense to say that they are acting against Jewish law?
I saw on Wikipedia, in the halakhic entry on this issue, that when there is danger in living in Israel one must fight for it even to the point of self-sacrifice. Doesn’t that contradict the permission to leave when there is a basis for assuming that it is in danger?
Thank you very much

Definitely yes. Halakhic decisors already wrote that there is a difference between not immigrating to the Land and leaving the Land. Something like this was written by the commentators on Maimonides in the Laws of Kings regarding returning to Egypt (he himself lived in Egypt).
Does the fact that many people do something make it permissible? Lots of people also speak slander. True, here some of those many people also think it is permitted (unlike slander), but still. Moreover, how do they think there is a prohibition if many people do it? Doesn’t the same question apply to them?
The commandment to conquer the Land, as distinct from dwelling in the Land, is incumbent on the community. Today there is no Jewish collective in that sense, and in my opinion there is no commandment to conquer the Land. Therefore all our wars today do not fall under the category of conquering the Land, but rather rescuing Jews from an enemy’s hand (that is, saving life). One implication of this (which I discussed in column 609) is the obligation of Jews from abroad to join.

Is there room to permit emigration and settling in another country even in a case where the person does not believe that the State of Israel is in existential danger, but living here causes him emotional distress for other reasons, such as a general fear of difficult security situations (which do not necessarily include existential danger to the state), a poor economic situation, a feeling of social alienation, and the like?

It’s hard to give sharp definitions here. There is permission to leave the Land for livelihood and to escape famine, and it seems to me that emotional distress is no less serious than those.

But isn’t the permission to leave the Land for livelihood and to escape famine only for the sake of a temporary departure? I’m talking about emigration and settling permanently.

That too is temporary. When the situation improves, he will return.

But is he permitted from the outset to leave with the intention of settling there, when he does not believe that in the future he will return to settle again in Israel?

What he believes doesn’t matter. What matters is what he does and why.