... the boats are often already sunk, without being discovered. If that's not stopping people, sinking more isn't exactly going to help.
Yes they will. Go look up what the smugglers advertise to potential customers; they detail which countries give what benefits, which countries have ID for illegal immigrant checks and working checks, which countries have the weakest borders - and for the all important meditteranean crossing they also detail at what point a red cross or coast guard ship will pick up your boat and bring you to Italy or Malta.
You take that boat and sink it, return everyone to their home country and you make it known all boats will be sunk. The boats will not be able to be reused. And as I said before, kill the smugglers and continue to do so until they are sufficiently discouraged with the knowledge that to attempt smuggling operations will result in their death.
This also ignores that countries which actually once had the ability to control their borders did not have mass immigration until, and this is not surprising in the least, parties in favour of mass immigration came into power or the countries lost control of their borders under the Schengen agreement.
I use Britain just because it's the country I know the most about, in the 90s immigration was around 50,000-80,000 people a year, mostly from the commonwealth. By the noughties it was increasing to around 150,000, still mostly from the commonwealth - but rising. Last year it was over
320,000 coming through the EU. It's never been this high in the entirety of British history.
Unsurprisingly when you allow everyone to move freely through Europe they're going to move through Europe. This is not an astonishing principle. And when you consider the extent of illegal immigration is never truly known, it's even worse. And honestly I can't even fathom what the rest of the European countries must be burdened with, because think of it this way; it's bad in the UK, but the UK is an island and you at the very least have to supply a passport meaning it is considerably harder to sneak in. Everyone else? Border control doesn't exist inside the schengen lands.
No, Europe just needs to realize that being well-off means that those who aren't want to move to the place that is. There's not much you can do about it, really. Boggle it down in bureaucracy?
Europe once had real border control, now has none. What are you talking about there's nothing much that can be done, when what was done worked and was always done until the EU decided to fuck common sense with a spiky baseball bat?