1. Because Trump called for an investigation into the Lab Leak Theory. Since Trump is bad, everything he says and does is always bad. This meant that everyone who was anti-Trump said that the lab leak theory was 100% false, definitely a consipracy theory and hence.... bad.
2. Because the Chinese government have used the modern political environment to deflect all critism as racism. Because people often shorten "Chinese Government" to "China" in news (much like the US), they take it that attacks against "China" aren't really attacks against the country but instead racist attacks against the people. Since racism is bad, criticism of China is racism, and investigating the Lab Leak leak is criticism of China - it stans to reason that the Lab Leak theory is racism, and hence.... bad.