It would be harder for the government to censor speech if their were more diverse venues for speech, yes.

But the real issue - the matter before the Court - is whether the government is abusing its power by directing the venues to stifle one type of speech and promote another. An injunction is issued when a judge deems the plaintiff likely to succeed on the merits, and the harm inflicted by the defendant’s actions in the meantime to not be redressable.