Would have been embarrassing to have the punk booed and have rotten fruit and tomatoes tossed at him during his welcome home parade.
They probably cancelled it because they don;t think he’ll shave his beard or wear western clothes.
I think this is the real reason why it was cancelled.
I'm don't think anyone would have been throwing things at him (that's assault), but you can be sure the parade would have been attended by many veterans and other people outraged by the hero's welcome for a deserter.
And they likely would have expressed their displeasure in various ways protected by the First Amendment.