If people refrained from being impolite to one another the condition of society would be greatly improved.
Conclusion
Society would not be better off if the government enacted laws requiring people to be polite to each other.
Evidence
Enforcing such laws would create even more problems than does impoliteness.
Evaluate
Whenever we read the argument in Role or Main Conclusion, we remind ourselves that in 85% of more of these, the conclusion is earlier than the evidence. Specifically, it's either - the very first claim - some sort of rebuttal / pivot
Could this first sentence be the conclusion?
Sure, it sounds like an opinion. . Does the author support that opinion. It's not a conclusion until it gets supported. Does she tell us why society would be better if people were polite?
No. If there were support for why society would be better if people were more polite, it would sound like,
The second sentence has a pivot word, "But", so this is also a ripe contender for being the conclusion. Is this an opinion from our author?
Sure. The opinion is that . Does the author support / defend that claim?
Yes, the final sentence supports it. We wouldn't be better off because enforcing politeness laws would create even more problems than our normal impoliteness does.
Goal
We're being asked about the second sentence, which was the Main Conclusion. So let's look for "Main Conclusion".