How can voluntary transactions act to the detriment of both parties? This makes absolutely no sense at all.
“Countries” don’t trade, individuals do. When individuals are free to engage in voluntary transactions, they will seek transactions tending to maximize their individual benefit.
Third parties who would seek to use coercion to restrain the freedom of individuals to make transactions may actually want to force them to make transactions benefiting themselves or may be misinformed and acting out of misguided humanitarian impulses. Or they may be well informed and want to use purported humanitarian ideals to force the parties to make transactions favorable to themselves.
In Sanders case, I believe he is well informed but champions misguided policies for personal political advantage.
No, he's just a Socialist Democrat... At least he doesn't run from the label. But HL Mencken has the better phrase for these people... the Demogogue:
"The demagogue is one who preaches doctrines he knows to be untrue to men he knows to be idiots."
That could be the Democrats campaign slogan.
Worth repeating -- I wish more people understood that.