I think proper, accepted terminology is very important. People have a perfect right to be called whatever they want to be called. This is understood in our humdrum daily lives, where we will ask a stranger what their name is, how to pronounce their name (if necessary), etc. We would never think of deliberately calling them names which are offensive to them (unless we are self-centered bigots).
Yet in religious matters, all of this is too often reversed. Not only are folks called names that they object to (and have for sometimes hundreds of years), but the people who do it try to justify it on absurd grounds. Examples of this are the derogatory, pejorative terms for Catholics, such as papist and Romanist.
I've never heard a Methodist object to that name. Often, Calvinists like "Reformed" better as a title, but I've never really heard one object to being called a Calvinist (and that word is used in many many of their own books). There are commonly accepted terms for groups, and they ought to be used. It is simple courtesy and charity.
We may call people a sort of alternate nickname (I do it myself) -- and this may be in a critical sense, or with an "edge" to it -- but it is important to note that such a nickname is not understood as their primary name or the one they themselves prefer to be called. Such alternate titles or nicknames shouldn't be routinely applied to large, historically and sociologically significant groups. Everyone knows what their real titles are. And that's the whole point about titles: they are based on common, accepted usage (much like dictionary definitions of words which are ultimately dependent on real-life usage.
It's true that sometimes we can legitimately war against a title, because a principle is at stake. Hence, I refuse to acknowledge the terms Enlightenment or the abuse of the term Dark Ages (when it includes even the late Middle Ages) because those are prejudiced, deliberately hostile terms which arose from secularist, anti-Christian schools of thought. I vigorously deny that the so-called Enlightenment was some great advance of civilization. It was quite the contrary.
But the terms Catholic or Reformed or Lutheran or Methodist are not such that they can be overthrown by the whim of personal opinion. I deny that Reformed are truly "reformed" from my perspective (which has to do with how Catholics define reform from within their own paradigm and ecclesiology -- the term is already inherently weighted against Catholic Tradition), but I accept the title because a title is a title. For that matter, I deny that Jewish Orthodox are orthodox (which means "correct belief"). But I use the term because that is what they call themselves.
Likewise, some Protestants may resent calling us Catholics because to them this implies that other Christians aren't "catholic" (in the sense of the Nicene Creed); yet this is our chosen title. We believe that our Church is uniquely universal, just as you believe that yours is truly, uiniquely "reformed" -- even over against Arminian fellow Protestants -- (whereas ours is supposedly not, in fundamental ways). Both schools claim unique characteristics for themselves which exclude others in some sense.
It's unavoidable. We all have beliefs, and someone else is bound to be excluded (or offended) by them. A different belief-system shouldn't, however, be immediately offensive (unless it involves hatred or some other sin). On the other hand, deliberate use of offensive terminology (based on the stated preference of a group so-called) is a different story. It is far more a matter of respect and politeness and diplomacy than of theology.
The use of terms like Romanist, papist, and (to a somewhat lesser extent), papalist, and the deliberate refusal to use the commonly-accepted and preferred Catholic, or to always (and for a particular polemical purpose) qualify it with the preceding "Roman" (which actually excludes some 21 non-Latin rites in the Church, and was originally derived from polemical Anglican usage in the 16th century -- in the attempt to be "catholic" without the pope) is, therefore, a condescending, uncharitable, impolite act, which offends the great majority of Catholics.
Why is it that Catholics are so often singled out by being referred to in ways that we have repeatedly objected to? To me, that is a dead giveaway that prejudice and some sort of strong hostility is in play, either consciously or unconsciously. No doubt many people do this out of force of habit, since it has been going on so long in their circles. But that makes it no less obnoxious for those of us who have to put up with this unnecessary, childish, and rather silly annoyance.