The english language is defined by use. Not by my use, but the general use in the english speaking community in general. This is very different from having no definition. I am trying to use it as it is generally used, not for moral pressure. If you want to define it I shall use your definition for the purposes of this discussion.
That's backward reasoning.
Any langage is defined by use on the long term, but that doesn't imply words don't have meaning. It just imply this meaning change with use (and, in this case, abuse). The emotional load of a word is based on its meaning, and it's precisely because of this emotional load that it's used as a weapon even when the meaning is not appropriate.
Abusing a word voids it of it's meaning and makes it useless for communicating.
I have been thinking about it (perhaps I should start by reading, but I have enough reading to do for work). It seems the most rigorous way is to define one's moral axioms and then work from them to practical actions. So you could start with some definition of utilitarianism. From there you could ask whether freedom of movement would increase the sum of happiness and well-being / reduce the sum of unhappiness and suffering. It seems to me obvious that it would, not least as it would reduce the incidence of wars if everyone had friends and family in all corners of the world. How to get there is certainly a question for a utilitarian, as it could cause disruption that harms people's well being, but the goal should be clear from this foundation.
First, utilitarianism is not morality, it's an attempt at efficiency. You can basically justifies anything, even the most heinous actions, if you can "balance the sheets". Propaganda is utilitarian. Scapegoating is utilitarian. That's a pretty terrible foundation to take if you're trying to speak about what is right/moral, because it explicitely doesn't care about morality, just about results.
Second, not it isn't obvious at all that complete freedom of movement would makes magically everything nice and cosy. I specifically asked you about the whole in-group/out-group and territoriality concepts precisely to remind you that they are normal psychological phenomenons, which go directly against large free movements of populations.
Few species tolerate encroaching on their territories (and humans are not part of those who do), and seeing people from the out-group coming in numbers is certainly NOT something that will go smoothly.
That's not even speaking of material problems, which are actually the subject of this thread, like housing and work and economical exploitation and so on.
You're simply ignoring the most basic human behaviour AND the blatantly obvious frictions visible all over the world when it comes to immigration here.
Others may take the teaching of Jesus as their axioms. It seems the most relevant would be the parable of the good samaritan. From that we could derive that we should treat those who come from geographically remote locations, are genetically distinct and have different cultures as neighbours.
That's not a reasoning here, that's just quoting Jesus. He might be right, he might be wrong, but this is not an argument, it's a "you should do this". The questions of the "why" and "is it good" aren't answered.
Both of these sets of axioms come to the same conclusion, we should not discriminate based on geographic origin, genetics or culture. As I said in the 2nd post of this thread, I am not aware of a set of acceptable (to me) axioms that would result in a different conclusion. I would be very interested in how you would derive a different conclusion. It is worth noting that I do not accept "everyone else thinks X" as any proof of X, as it has been shown to be wrong too many times, both historically and personally.
Your first axiom is downright false, the second is an appeal to religious authority. I'm still unconvinced (to say the least).
My take on morality : any morality that isn't applicable to actual humans, is crap and worthless. If you need to rewrite humans to be fundamentally different to make your system work, then it's wishful thinking, not something applicable.
Of course,
ideals are fine, because they are by definition unattainable
goals that people should strive for to improve themselves. But if Regular Joe can't reach the "good enough" without chaning his human nature, then it's not morality, it's brainwashing.
As such, morality needs to take into account that humans have in-groups and out-groups, and feel territorial. People dislikes when strangers encroach on their turf. People takes time to accept a newcomer in their group. People creates culture with time, and they are attached to it. All that is normal and not immoral as long as it's kept in check by not letting them act unjustly toward others due to prejudice.
Trying to ignore all this and shout "RACIST" in order to shame people into complying is actually what I see as much more immoral - not only it is intellectually dishonest, it also basically means you want to enforce imaginary standards to actual humans (notice that I'm speaking of the ABUSE of the word here, not shouting "racist" when the person is ACTUALLY racist, hence the importance of actual definitions and remembering WHY "racist" is actually bad, rather than letting it be applied nilly-willy). And even if you go with utilitarianism BS, it also simply fails in practice, as we can see in the serious integration and migration-related troubles that arise (it's what the OP is talking about after all).