1.- So your point is it that it would be impossible for your (or any boat) to travel to some far-flung port, pick up a hitchhiker and then (not having cleaned the bottom prior to returning) bring it back with them? You can't understand how this would happen? Seriously?

2.- Again (I guess I should get used to repeating myself with this crowd), the point is to remove the potentially invasive species before you transport it. After you've arrived doesn't do a whole lot of good, does it?

3.- See number one.

4.- Good question. But the fact that a haulout isn't required (and really, how would you enforce that one?) doesn't mean there isn't a problem.

Please follow the link and educate yourself a little bit.