The idiom for "slander what you believe in" is "casting stones in glass houses." This phrase is used to criticize someone who is attacking others for their beliefs or actions while having similar flaws or being guilty of the same offense. The idiom metaphorically suggests that the accuser is living in a glass house, meaning that they are vulnerable to the same criticism they are leveling against others.

This idiom is particularly relevant in the context of political discourse and social media, where individuals often attack others' beliefs or actions without acknowledging their own similar shortcomings. According to a study by the Pew Research Center, 81% of Americans believe that political polarization is a major problem in the country, and 69% say that social media has contributed to this polarization. The use of "casting stones in glass houses" serves as a reminder that individuals should be cautious about attacking others' beliefs without considering their own actions and beliefs.

The idiom also reflects the human tendency to focus on the faults of others while ignoring or excusing our own. This cognitive bias is known as the "fundamental attribution error," where people attribute others' behaviors to internal characteristics rather than situational factors, while attributing their own behaviors to external circumstances. A study published in the Journal of Personality and Social Psychology found that people are more likely to commit unethical behavior when they believe they will not be held accountable, suggesting that the idiom "casting stones in glass houses" can serve as a cautionary tale against such behavior.

In conclusion, the idiom "casting stones in glass houses" is a powerful tool for highlighting the inconsistency and hypocrisy in attacking others' beliefs while ignoring one's own. It serves as a reminder of the importance of self-reflection and the need to hold ourselves to the same standards we apply to others.