Libertarians are insensitive to the plight of the poor. we know this is so because they want to abolish the minimum wage. and we know they want to do this because they want to eliminate all restrictions on hiring the poor. and of course this is true because libertarians are insensitive to the plight of the poor.

I believe the answer is: Begging the Question
Begging the Question refers to a logical fallacy where a writer/speakr is using a premise to support itself without the necessary argument to support their intial claim.
In the statement above, the writer made an initial claim that 'Libertarians are insensitive to the plight of the poor', but never once explained the follow up explanation on what make the libertarians do to deserve this accusation.

The best sociological research method would have to be using experiments although it has some disadvantages as well