Deontology is, alongside Utilitarianism, one of the most common philosophical frameworks in debate.
If you recall, utilitarianism is the idea that we should strive for the most good, for the most people— and ‘pure’ or classical utilitarianism doesn’t particularly care how we get there.
In other words, if we have the chance to kill baby Hitler, we certainly should: its seems quite obvious that the world would be a better place without Hitler (although time-travel movies should make us think twice!).
Deontology says, in essence, that there are some things that are just good— and others that are just bad. Our moral code shouldn’t come from our personal judgements about how our actions improve the world— after all, if we all used personal judgements to justify things like baby-murder then our world would clearly be chaos.
So, according to deontology: don’t kill babies. Even if you think they might be evil babies.
Respect of human dignity, and human life in particular, is therefore a ‘line in the sand’ for deontologists. Humans shouldn’t objectified or used as resources, despite the apparent good you hope to do in the world.
How could this philosophy be applied to debate? In debate we often have to weigh policy not according to if it’s good or bad, but according to the weighing of its positive and negative effects. Because, of course, every policy has a ‘good’ and a ‘bad’ side, tradeoffs that are simply part of life. Often, social programs come with high price tags. And humanitarian interventions come with a decrease in sovereignty or even a high death toll.
So, if your opponent proposes a policy that, while seemingly reprehensible, will have even more upside than downside, you can invoke deontology to explain to the judge that, no— some things are just wrong, especially given our inability to truly know the long-term repercussions of our actions.
Of course, moral philosophers have built entire careers out of exploring the thought experiments and edge cases around both of these philosophies, so these few paragraphs are a gross over-simplification. For further information on deontology, please consult the ol' Googz.