And criticisms of alternative theories must always be done scientifically rather than dismissively.

Only if they're presented scientifically, i.e. they explain observed phenomena at least as well as the current prevailing theory.

Too often people use the term "theory" in scientific arguments in a colloquial sense that means nothing more than "my political beliefs or preferences"

There's no obligation though to respond with scientific rigor to a collection of claptrap that someone may have pulled from their backside.  Google Brandolini's law.