A word for a “troll” who is actually advocating a point of view

Solution 1:

The late Christopher Hitchens was a primary example of a gadfly:

2 : gadfly, n.: a usually purposely annoying or provoking person; especially : one who stimulates or provokes to activity and especially to the analysis and defense of ideas by persistent criticism especially of an irritating pointed kind

Or, more formally (as noted in the obituary at the link), a polemicist:

A person who engages in controversial debate

Solution 2:

I think of the word "blowhard." Here is the Wiktionary definition:

(derogatory) A person who talks too much or too loudly, especially in a boastful or self-important manner.

There is also "zealot." Wiktionary Definition:

One who is zealous, one who is full of zeal for his own specific beliefs or objectives, usually in the negative sense of being too passionate; a fanatic

Or "firebrand." Wiktionary definition:

An argumentative troublemaker or revolutionary; one who agitates against the current situation.

Each of the three words I've provided have a negative connotation; they are not compliments.

Solution 3:

A dogmatist is someone who "express[es] personal opinions or beliefs as if they are certainly correct and cannot be doubted" (Merriam-Webster), so that sort of person would by definition be staunchly dismissive of any opposing views.