In a 'This House Regrets' motion, Team Proposition is expected to step back in time to when a specific event or thing happened, and argue that the world would have been better without it.
Example: THR the rise of social media as a primary news source.
Here, Proposition could argue that the world would have been better had traditional/legacy media (such as newspapers, tv, radio) remained the main source of news.
Team Opposition is expected to defend the current state of the world, aka the status quo.