There is no excuse or reason why a group should face persecution. However, the most basic reason why the Chinese regime started to persecute Falun Gong is that is what violent dictatorships do. It is what they have done to Tibet, it is what they did to the student democracy movement and also what they have done to the Uyghurs and the Christians in China.
That being said, there are several interconnected factors and dynamics that can help shed light on how this specific persecution befell China.
Falun Gong’s rapid growth and independence
Since Falun Gong’s introduction to the public in 1992 its practitioners numbered over 70 million in China in only seven years based on Chinese government statistics. As the US News and World Report put it in 1999, Falun Gong had become “the largest voluntary organisation in China, larger even than the Communist Party”, whose membership at the time stood at 65 million. The totalitarian Party saw Falun Gong’s independence and ability to coordinate activities a dangerous precedent, even if those activities were fundamentally apolitical and beneficial to Chinese citizens.
Jiang Zemin’s intense jealousy
Jiang Zemin was the leader of the CCP at the time. With a handful of supporters, led by Luo Gan, Jiang dictated the anti-Falun Gong stance by presenting the group as "the biggest threat to the Party", labelling Falun Gong an “evil religion”, creating the 6-10 Office, and pushing forward legislation to retroactively justify the ban.
There are two reasons why he did such a thing. First, journalistic accounts and inside sources suggest that Jiang was acutely jealous of Falun Gong’s popularity and saw it as undercutting his own legacy.
Second, as CNN analyst Willy Lam and others have suggested, Jiang saw an opportunity. By attacking Falun Gong and creating a Maoist-style campaign, Jiang could use the campaign “to promote allegiance to himself” and to manoeuvre for political gain. (see CNN report).
Why has the campaign continued so aggressively even after Jiang's retirement? Jiang arranged for members of his political faction to remain in top positions within the Politburo and Party security apparatuses. These people have been able to maintain and even intensify the campaign. Reports from inside China, however, do reveal increasing tensions between Jiang’s faction and the new leadership.
Also, these officials may now fear responsibility for crimes against humanity; thus it would be in their best interest to cover up these crimes by continuing the persecution.
The ideology difference
All religions and spiritual practices in China must place belief in the Communist Party over their belief in their chosen faith, and thus many faiths that refuse continue to be persecuted today.
Some Party leaders feared that Falun Gong with its principles of truthfulness, compassion, forbearance and its belief in Buddhas, Daos and Gods was in conflict with the Party's ideology. The Xinhua news agency, the official mouthpiece of the Party, reported shortly after the persecution was launched: “The so called principles of truth-goodness-tolerance that Li Hongzhi (Falun Gong founder) propagates have nothing to do with the socialist, ethnic and cultural progress that we pursue.”
In addition, the Party-top feared that Falun Gong's moral code undermined the Party's communist tactics for controlling society. Where Party-controlled media deceive the public, Falun Gong emphasises truthfulness; where the Party calls for people to struggle against each other, Falun Gong urges kindness; and where the Party uses violence to enforce its will, Falun Gong teaches strict nonviolence.