I can't answer to legality since IANAL and systems vary anyways, but on a moral basis, yes, it is absolutely nonetheless unreasonable until SpaceX / Starlink actually commit an actionable offense of their own or otherwise demonstrate the intent to do so. It's outstandingly unreasonable and offensive to seize assets of such an entity without charging that specific entity with an offense; especially so when your basis is literally "I want to compel an unrelated venture with common beneficial ownership to unilaterally censor my political opponents worldwide".

AFAICT, Starlink complies with local regulations in the countries it operates in, including blocking access to specific IP prefixes and/or declining to default resolve DNS entries for specific domains.

Yes it is unreasonable. It's only reasonable from an authoritarian perspective.