..."dogma of the Immaculate Conception.....tells the believer that Mary is merely human and subject to the contamination of original sin; this stain only removed by Father-god"......

Yes, of course. According to Catholic teaching over the years, Mary also is 'subject' to it, but 'saved' from it, by the Sacrifice of Jesus. 

Of course now that we have begun to understand that God inspired the Creation stories of Genesis to be written as a myth literary form, we really need to do some re-thinking about our notions of 'original sin'. 

Since 'Adam and Eve' are only mythical people, they never existed, historically. Neither did their 'sin'. There was no one to commit a sin' to inherit. So it follows that: of course Mary was conceived without 'original sin' And she is the model for us all. EVERYONE  is conceived and born without 'original sin', because there WAS no original sin.

And, of course, Mary is not supposed to be made into 'the great goddess'. She is as human as we all are,