To me, for all practical purposes, there is a difference between
dogma and being dogmatic. Dogma, meaning a religious doctrine or system of doctrines proclaimed by the collective Church throughout the ages as authoritatively true. This word is legitimate, as long as it stays in the confines of its corral (context). But when it jumps the fence and goes wild by asserting its own individual unproved doctrines as truth, its name changes to dogmatic. Such are characterized by an arrogant, egotistical, and overbearing spirit.
A dogmatist simply takes sound dogma too far. They take a good thing to extreme until it is distorted and unrecognizable. For example: the sovereignty of God and the free will of man; faith and works; God's love and His wrath; doctrine and devotion; the local church and the true Church; etc. There are always two extremes, two dog houses, if you please, each at opposite ends of a truth and far apart. Each take one side of that truth and run off to their doghouse to feed innocent pups. There is no middle ground with a dogmatist; only his or her way or the highway!
But having said all this, as despicable, detestable, and hideous as these dogmatists are, we owe them a debt of gratitude. Because, for the most part, many of us can attest to the fact that because of them we found our scriptural balance by observing where their teaching leads one. And it lead us back to the middle, thus saving our spiritual sanity.