What words we use to describe something can make a big difference to how we view it. In the initial stages of a debate, you should try to frame the debate in a vocabulary favourable to your position.
For example, there are many different ways to describe someone being overweight; they could be "fat", "chunky", "obese", "chubby", "plump", "cuddly". If you are arguing that someone should get more exercise, then you want to discuss what they should do about being fat (or preferably "obese"); if you are arguing that they should be allowed to do whatever they want, then you want to discuss whether it matters that they're cuddly.
Similarly, if you're arguing that we should prosecute people for taking bread from the supermarket to feed their family, then you want to discuss this in terms of whether all thieves should be punished. If, on the other hand, you are arguing that people who do such things shouldn't be punished, then you want to discuss what we should do help our loved ones when they're facing starvation.
Don't let you opponent set the terms of the debate. Pick your phrases carefully, and pick them early.