Moral arguments aren't typically persuasive against people with differing values or interests. They rely on a value system, and to refute a value system all you have to do is respond with a different one, which is what has happened here. Or all you have to do is to further en vague the arguments that are all ready vague, which has also happened here.
Practical arguments work, however. There is always a winner. Your options can be reduced to those that have the most desired results that can be foreseen, or you can identify groups or person with the most power and predict that the outcome will serve their interests or result in a conflict.
And while I think Bief is just trying to give a moral face to a practical argument, I am going to give a practical argument.
(PS: This argument doesn't necessary pertain to me, but it is a practical argument that would be popular imo.).
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Personally, I have reason to be inconvenienced by some groups that were allowed to immigrate for the long-term, especially ones that were allowed to enter without merit. These groups tend to live in poverty and leech off of the state, are more likely to be prone to criminal activity because of their poverty, and at other times they add competition for jobs. Furthermore, they concern me as a growing center of power. With such indiscriminate immigration, this impoverished group can gain power in our democratic system at my expense.
I understand the need for immigration or work visas in our country, but restrictions need to be instituted. In the case of immigration, I only want persons with merit and good behavior to take permanent residence in our country. In the case of persons of working class or impoverished origin here on a work visa, I want all such persons closely monitored and filed. We moreover only allow such persons to live and work in our country when our economy is performing well and there is a scarcity of labor. Should they ever misbehave, they will be immediately deported. Moreover, I want priority given to a citizen applying for a particular job over one working on a work visa, assuming the citizen is equally or similarly qualified for the job. In the event of a recession or depression where there becomes a scarcity of jobs, we will deport all appropriate persons working on a work-visa and suspend the program. In the case of an applying immigrant who is well-off, well educated and well-mannered, we may consider giving them citizenship and allow them to participate in our democratic government. Furthermore, persons in our country with a working visa who are classified as working class will not be considered for citizenship, under any circumstances.
Keep in mind this is all about self and group interest. No matter what moral arguments you shove down such a person's throat, they will say "it's not in my interest, and I will consider my best interest."
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Bief, I suggest you take this line of reasoning. It's more clear and it allows actual progress to be made in the argument. At best your opponents can try to do is try to reach a compromise, or at worst agree to disagree or flip out on morality lol.