1) In a perfect world (one with only baptists
), there probably would be little to do about such doctrines. Chances are they would never come up. I think the reason they come up so often is simply because we don't live in a monotonic world, with everyone echoing the same ideas, but one that is very diverse. Within that diverse world there is significant disagreement over this issue precisely because Rome in particular has declared these things as dogma, essentially tying them into the gospel itself and salvation (in the sense that EENS would normatively require membership in the church, and membership in the church requires assent to all dogmas). As such, there is significant division over this issue because of that. I think if Catholics held these beliefs but never declared them dogma, there would not nearly be so much rancor over them, though it might still exist.
2) A distinction should really be made between marian doctrines as well. Some, such as using God-Bearer or the perpetual virginity, do not really raise that many hackles as they aren't really that theologically significant in defining the theological boundries of various churches. This is quiote different from doctrines such as Mary as the mediatrix which involves a very different conception of grace of salvation itself that the protestant perspective. As such, we react strongly to such ideas.
3) As our attitude is to stay as much to the scriptures as possible, the marian doctrines in large measure create tension because they push the boundries of this very hard while simultaneously being advanced as required belief (which makes them tied into salvation by implication as I illustrated above).
I think my arguments above show this. Ultimately it comes down to this - that we do not believe as a general rule that one should bind the conscience of a believer with doctrines the scripture has not revealed. Of course, baptists are not always stringent in application of this principle, but nonetheless we do try not to trangress such things. As Rome has bound the consicences of believers to these doctrines, and requires consent to them in a normative sense for salvation (through membership in the visible church), we cannot help but be opposed to such teachings.
ken