I find it's pretty easy to frame the debate, generally, though. When they bring up off-topic points, you say "There's plenty of room to discuss those issues you brought up, but I'm still interested in your thoughts on my original question."
Now, you become an annoying ass when you try to turn every discussion into a debate, and try to win every time. Don't do that. Sometimes it's better to let other people win or just feel heard. But if you want to win, that's how you do it.
> ... you say "There's plenty of room to discuss those issues you brought up, but I'm still interested in your thoughts on my original question."
But you just said your M.O. is to deliberately force the opponent to operate in a "tiny airspace" that you define. So, there's not really "plenty of room" to discuss those issues they brought up.
That pisses people off, it's seen as an aggressive move and can easily backfire.
Framing the debate is perhaps the most difficult task towards "winning" a debate.
I think you might be misinterpreting what I'm actually describing. I agree -- you should not try to debate people in casual conversation with the goal of winning. Even if they're logically incorrect in a few places, their underlying values are still valid, so you need to work with them to find a solution that works for everyone.
Trying to "win" can definitely backfire, so you should do it sparingly. In truth, the only place I really debate people is on the internet, most visibly with my pro-Trump relatives on Facebook :).
However, the person I was responding to was talking about "how to win debates," and that's how you do it. Yes, if you want to win, you do need to be hard nosed and aggressive (I prefer gently guiding them down the garden path until they realize it's too late to turn back). Whether or not you should do it is a different point entirely, and to be frank, I completely agree with you there.
(Meta note: do you see how I'm actually making a belated attempt to frame the debate right here, and it's not necessarily as aggressive as I describe? Really sometimes it's just needed to establish clarity.)
Now, you become an annoying ass when you try to turn every discussion into a debate, and try to win every time. Don't do that. Sometimes it's better to let other people win or just feel heard. But if you want to win, that's how you do it.