> The only way to stop them is to discourage them from getting in the boats in the first place.
Which does not work because to quite a lot of people drowning in the Channel is preferable to what they fled back home if there is the tiniest of chances that they can actually make it to a place where they or their children can actually make a living. This line of reasoning is like "let's use harder punishments to dissuade the others". It never worked that way, and still does not now.
> The point of the Rwanda scheme is to make getting in the boat an undesirable option, because you'll just end up somewhere you don't want to be.
That's not the calculation they make. Their issue is being shot at, disappeared, bombed, or tortured if they stay. Most of the time their risk analysis does not go beyond leaving the country and you see quite a lot of them drifting from country to country once they are in Europe. The ones who show up at Calais are those who come from former regions of influence of the British Empire. No amount of dissuasion is going to change that.
> The hope is that few people will have to be sent to Rwanda because they'll stop paying people smugglers to make the trip.
It won't work and they won't stop. Again, these people take risks assuming that they have a chance of not being caught or to actually get granted asylum once they arrive (fat chance; most of them don't have a very accurate image of the UK). How is the British government paying to export them to Africa going to change anything in this calculation? Could the UK actually pay to deport all these asylum seekers? Could Rwanda actually welcome them in anything that looks like decent conditions? The most likely answers are "no" and "no", and the examples of Australia's refugees camps out in the Pacific are really not encouraging.