There are a number of synonyms for the phrase "are down on," all of which express a negative or critical sentiment toward something. Some possible options might include phrases like "have a problem with," "are critical of," "are negative about," "are unsupportive of," "are opposed to," "are against," "are disapproving of," "are displeased with," or "are unhappy with." Depending on the context or tone of the conversation, other synonyms could include terms like "are hostile toward," "are derogatory about," "are disdainful of," "are dismissive of," or "are disdainful of." Ultimately, the choice of synonym will depend on the specific context of the conversation and the speaker's intended message.