What in the constitution demands that the feds "publicly communicate" their reasons? I haven't really followed the story terribly closely, but it seems some aren't starting with the assumption of innocence. They are starting with other assumptions.
IF they burst into his home and arrested him, with no warrant, for words that did not include inciting violence or other unprotected speech, then I agree with you. But all this argumentation can probably simmer for a bit until and unless we get a lot more facts than media claims.