I dont know though is that becauase of a distaste for religion per se, or if its more a feeling that churchmen are stuffy and boring, not fashionable, They are prudish and dull, and generally speaking a clergyman isn't going to cut a figure in society or become very rich....

I think that Mary wants a husband who is a fashionable gentleman partly because of the money side of it and partly because she enjoys that sort of London life of partying, gaiety and socialsing... and she cant imagine any other...
As the wife of a politican or an upcoming lawyer or just a wealthy society man, she could have more of a role as a hostess which she would enjoy, wheras the wife of a clergyman is someone who must sink herself in the dull side of her husban'ds job, and I thnk that M cant imagien herself doling out clothes to the poor and listening to sermons and so on...