I don't think that's best modeled as reflecting Republicans' willingness to censor in general, because they're less likely to support criminalization on all other questions. To me it looks like they make an exception for speech that they believe could theoretically destroy the government altogether. That's understandable, even though I disagree that we should see flag burning as a threat. It's as if I could precisely predict desire for sweets by comparing likeability to sugar content for a wide range of sweets, but not for strawberry tarts. We'd be justified in thinking that maybe sugar content matters a lot but strawberry tarts are just a weird aberration because you're allergic to strawberries, ie your immune system goes haywire when exposed to them. We'd be wrong in thinking this indicates you dislike sweets altogether.