How can you be sure you won't provide bad counseling due to your prejudice in FAVOR of them?

I disagree because I think as a counselor you should be neutral. You should not like or dislike your clients based on identity.

Gender is an identity.

Like: feeling of liking for another person; enjoyment in their company. approval. a feeling of liking something or someone good. admiration, esteem. a feeling of delighted approval and liking.

This isn't appropriate in a professional therapeutic environment based solely on identity.