Why do Evangelical Protestants reject the Catholic approach to venerating Mary? When Elizabeth greeted Mary -


  42 ...she exclaimed with a loud cry, "Blessed are you among women, and blessed is the fruit of your womb! 43 And why is this granted me, that the mother of my Lord should come to me?..."  - Luke 1:42-43 (RSVCE)


Why don't Evangelical Protestants treat Mary with at least this much reverence?
Born-again protestant Christians are not "against" Mary of Nazareth. Every one of them accepts Mary as the Mother of Jesus, and while few would use the phrase, they have no issue with the concept of Mary as the Mother of God.

That said, all but a few protestants, including nearly all who would self-identify as "born-again" reject most of the teachings about Mary that have been defined over the years, mostly by the Roman Catholic Church, as being at best, unnecessary for salvation, since for the most part, most Protestants agree that (as Article VI of the Articles of Religion of the Church of England states): 


  Holy Scripture containeth all things necessary to salvation: so that whatsoever is not  read therein, nor may be proved thereby, is not to be required of any man, that it should be believed as an article of Faith, or be though requisite or necessary to salvation.


For protestants, principle rules out such teachings of the Roman Catholic church as the immaculate conception, the assumption, the notion of Mary as the mediatrix of all graces, and most Marian apparitions. Further, some of the teachings about Mary that are firmly grounded in Holy Scripture, like the annunciation, are not widely observed by many protestants, because they are not perceived to be of as much value in protestant theology.