That said, if people who haven’t harmed anyone are being imprisoned solely because of their beliefs, regardless of how poorly informed those beliefs are

Falun gong was indeed hurting people, not the least of which being its own members, including a child, who immolated themselves (or in the kid's case was almost murdered) as an act of public demonstration -- to say nothing of the harm they try to do to the public by denying the science of vaccines in general and covid vaccines in particular, their opposition to interracial marriage (because apparently heaven is racially segregated), their belief in breathing exercises replacing real medicine, etc.

Here's a fun little podcast thing about some of their projects