How do you propose that we don't let them in when they can buy inflatable boats in Calais and set sail?
"Stop the boats" is empty rhetoric.
At least when they turned up by lorry, they weren't drowning and weren't putting RNLI crews at risk. And no, we can't just tell the RNLI not to rescue them. a) That's not how maritime rescue works and b) the RNLI have no means of distinguishing whether a callout is for a boat full of migrants and a boat full of people on a fishing trip.