so why do you like mary

Take it from the leading men:

• “Miss Morstan and I stood together, and her hand was in mine. A wondrous subtle thing is love, for here were we two, who had never seen each other before that day, between whom no word or even look of affection had ever passed, and yet now in an hour of trouble our hands instinctively sought for each other. I have marveled at it since, but at the time it seemed the most natural thing that I should go out to her so, and, as she has often told me, there was in her also the instinct to turn to me for comfort and protection. So we stood hand in hand like two children, and there was peace in our hearts for all the dark things that surrounded us.” — John Watson, The Sign of the Four
  
• “I think she is one of the most charming young ladies I ever met, and might have been useful in such work as we have been doing. She had a decided genius that way.” — Sherlock Holmes, The Sign of the Four

Mary Morstan is a gem. First and foremost, she makes John happy. That much is already enough to convince me; Watson is my darling, and if she helps to fulfill his life, then I am sold. Sherlock himself also notes her charm and intelligence. High praise from him, to be sure!

Not to mention the fact that Mary is a goddamn angel. People that ship Sherlock/John and loathe Mary just because “she is a woman” or because “she gets in the way” are off their rockers, to be frank. I have heard those arguments a number of times, and that logic is so degrading to women, to Mary’s relationship with John, and to John’s relationship with Sherlock. For John, Mary fills a gap that Sherlock cannot. Mary and Sherlock complete John together. And I myself ship Sherlock and John in a number of adaptations! Mary supports John’s friendship with Sherlock and is beyond understanding of his loyalty to him. Mary also (spoiler!) dies in canon, so it is not as if she “keeps him from Sherlock.” John ends up back with him, regardless.

Mary is loving and empathetic and supportive and charismatic and witty and intelligent and I just cannot. I adore her.