I haven't played much but I feel about the migrants the same way as the original poster. They're like unwanted relatives dropping by. And they just keep coming no matter what...
Enough. I see it as my duty to list all the ways I've read about, or can think of, that may or may not stop or hinder the migrant flow to your precious fortress, the fortress started by the First Seven.
Whether these ideas work or not, is beyond me. I haven't really tested any of these. Here we go:
1. Tweak the [POPULATION_CAP:200] in /data/init/init.txt
If I understood correctly this should be first thing to try, but it seems to be iffy. So it might work more or less perfectly.
Perhaps one could attempt to reduce the TOTAL_CIV_POPULATION, too? (when creating a new world) (see /data/init/world_gen.txt)
2. "Unforeseen" "accidents"
There are many many bad things that could happen to a careless migrant dwarf (they're up to no good anyway). Off the top of my head I can remember/think of:
- Trapping and drowning them, somewhere along the way to your fortress (fascist)
- Really, just trapping them in one place is a big step. See if they die of hunger or thirst. (you despot, you)
- Try and get them trapped somewhere outside your fort, then wait for the next goblin wave or something. Ideally, any other outside threat might deal with the migrant nuisance, provided you've walled off your fort properly. Prepare popcorn and enjoy the show (sadist)
- Dwarves love to fall down the wells, don't they? Well, cordon them off in an area where there are a lot of wells... like the ones you've built for this specific purpose. Just make sure they're really deep.
- Deadly cave-ins could happen to anyone. Especially to migrant dwarves. (racist)
- If I understand correctly, some dwarves can go insane and start killing the other dwarves. Be prepared to overlook a murder or ten that take place when you've tricked that lazy migrant into the same room with the homicidal dwarf..
- Try and trap a really savage creature, and direct the unwanted dwarf in the same room with that creature. Essentially the same trick as with the Homicidal Dwarf -scenario but bit easier to produce, I believe.
- etc. etc.
3. Don't let anyone in!
This one sort of came up already, but I'll say it again: isolate your fort. Don't LET the migrants in. Build walls. Build doors. Build moats. Build lava moats. No bridges. Induce cave-ins that seal off your precious fort of the First Seven. There might come issues with pathfinding and laggier game but.. idk really. You'll have to try this unless you can think of why this wouldn't work. (antisocial hermit)
4. The 1x1 tile island
Someone wrote an interesting idea about attempting to find an island that's 1x1 in size as a starting location. Allegedly then you'd get no migrant dwarves. I'm not entirely sure how one would get the First Seven out of that island and start building things. Stairs down few z-levels followed by tunneling? *shrug*
5. Apply economic pressure on the (filthy) migrants
I read that dwarves might leave if they can't afford to live in your fort (?) So why not give them a really expensive room and see how long they last. (bastard)
Anyway, I guess I gotta do some reading. There's so much I don't know about this (spectacularly complex and detailed) game.