When expressing dissent or disapproval, there are a variety of ways to express your opposition to something that don't involve using the phrase "I am against." Some synonymous phrases you can use include "I object to," "I disagree with," "I'm not in favor of," "I oppose," "I take issue with," "I resist," "I am not for," "I cast doubt on," and "I dissent from." Each of these alternatives can help you convey your opinion while also adding some nuance to your language, making your argument more impactful and convincing. Using a diverse range of synonyms can help you sound more articulate and effective in expressing your point of view.