Conservative politicians often use the term as a way to negate their opponents positions on scientific or social issues.
Why do they do this ?
Often in the USA, Republicans or conservaties are associated with Big Business, such as oil companies. If environmental regulations are strengthened to combat climate change, these companies would lose a lot of their profit.
So, it is a good idea for such companies to hire scientists to "debunk" (to expose something as being fake) Junk Science which may have an effect on their business.
This being the case, you might see a respected scientist stating in an interview that the earth is not getting warmer but is actually cooling, or even if the earth is warming, it's actually a good thing for mankind.
Gun groups in America also use "Junk Science" to call into question statistics which may show that gun crimes are rising...
The American people are sometimes easy to manipulate by using such labels because the average person is perhaps not so well informed about science, and lacks the ability to determine which facts are true and which are "Junk"... (G.K)
as a way to negate 〜 〜を否定する手段として
associated with 〜 〜と結びついている
This being the case そういう訳（事情）で
good thing for mankind 人類にとって良い事
call into question 疑問を呈する、異論を差し挟む
easy to manipulate 操作されやすい