The federal government has a very poor track record of ensuring that only genuine threats end up on no fly lists or terror watch lists. Being on a watch list alone shouldn’t prevent a person from boarding a plane or cruise ship unless they've been convicted of terrorism.
What good is a no fly list if people on it are still able to fly? The terror watch list and no fly lists are imperfect and people have been mistakenly included, but the federal government should be able to use them to prevent people from boarding a plane or cruise ship.