So, the motion is
This house would restrict everyone to one long haul flight a year
You're the proposition. How should you engage with the opposition?
Obvious. Make out that anyone who opposes this motion is a callous, selfish monster who puts their own selfish pleasure before the future of the planet. Say that there is no excuse for anyone ever to fly anywhere. Point out that, given the likely consequences of climate change, anyone who so much as sets foot on a plane is little better than a murderer. That way, you will establish a clear dividing line between you and the opposition and, in the process, make them look so bad that you can only look good.
This way of argument is known as polarising, meaning the attempt to drive people as far apart from each other as possible, so that there is no common ground left. It is, unfortunately (and dangerously) very common in political discussion these days (particularly on social media). It is a way of arguing that means that only one side can win, and only through the total destruction of the other side. It is poisonous for society.
But a debate is a competition. The point is to win. Surely destroying the other side is what we should be doing, isn't it?
Wrong again. You are actually far more likely to win a debate (and to be a better citizen and a nicer person) if you find as much common ground as you can with your opponents.
So, in the debate on restricting access to long-haul flights, assume (and say) that the opposition are surely as concerned about climate change as you are; you just have a better plan for tackling the issue. Acknowledge that there are all kinds of good reasons why people might need to take long-haul flights. They may have family in faraway lands who need and depend on them. They may have essential and worthwhile work that they can only do in person. Mitigate the opposition's objections as much as you can through the construction of your mechanism. So you might say that exemptions will be granted for compassionate reasons, for example if a close family member is ill or has recently died in a country that can only be reached by a long haul flight, or for certain kinds of workers, for example aid workers responding to a natural disaster. Or you could propose a system of 'flight trading' whereby people who either don't want to or can't afford to fly long haul can sell their allocation to wealthier people who want / need to fly a lot.
All right, you might say, this is a better way to find agreement; but how is it a better way to win a debate?
Debating isn't just about attacking the other side's case; it's also about defending your own case. And the less there is to attack, the easier it is to defend. So, if you get as close as you can to the other side's case by agreeing with them as much as you reasonably can - in this case by accepting that long-haul flights are sometimes necessary, and by finding ways to allow people who need to take them to take them - the harder it is for the other side to attack you. All the opposition has now got left to attack is the principle that the total number of long-haul flights needs to be reduced. The only way to do that is either to come up with a better counter-mechanism for reducing the impact of flying on climate change (difficult), to argue that some people's freedom to fly is a higher good than every person's freedom from the consequences of climate change (very difficult) or to deny that flying has any impact on climate change (impossible).
If you'd gone for a full on assault, denying any merit in the case for allowing people to fly freely, it would be much easier for the opposition to attack your measure simply by putting the case for the necessity of air travel. By meeting them in the middle, you have made life much harder for them. Being nice is a good way to get what you want.