I don't think there is anything wrong with having ideals and high standards, but the standards Marianne has set for her self are not only unrealistic, but probably also not the best thing for her.

If we break her speech down, we can see this:

I could not be happy with a man whose taste did not in every point coincide with my own. He must enter into all my feelings; the same books, the same music must charm us both.

In other words, Marianne believes that she could only be happy with a man who liked everything she liked and who disliked and disapproved of everything she does not like (that would be a long list!). Is that realistic? Suppose she found out that a man like a particular piece of music or had enjoyed a book she didn't care for, but in all other respects was wonderful, should she write him off?

If they only are allowed to like the same books and music, how can they ever expand their horizons and learn anything new? If a new book came out, how would they know if they were charmed by it until they both read it? And what if one of them didn't like it? Would their relationship be over? Or would Marianne vow to never be happy again because of it?

She speaks in a language of absolutes. It's all or nothing with her. We're told when we very first 'meet' her in Ch. 1 "her sorrows, her joys, could have no moderation".

Just after the 'I require so much!' Marianne also says, "He must have all Edward's virtues, and his person and manners must ornament his goodness with every possible charm." Marianne's requirements extend not only to taste, but also she wants a man who is a good person, like Edward. However, for her, this must all come in a very attractive package. The guy has to be very gook-looking on top of all these other requirements.

She's very picky about the looks and manners. Even though she likes Edward, she says of him, "His eyes want all that spirit, that fire, which at once announce virtue and intelligence." In other words, if a man is not in raptures over the same things that Marianne admires, he will not have that fire in his eyes, and if that is not there, then he is lacking in either virtue or intelligence or both. Is that realistic?

Even though Colonel Brandon gives her musical performance more attention than anyone else does in Ch. 7, Marianne's thoughts are that " His pleasure in music" did not amount "to that extatic delight which alone could sympathize with her own".