With first-past-the-post, after a candidate receive party nomination, every candidate is incentivized to get the most votes possible. This usually means if there are two sides to an issue, both candidates moderate as much as possible to pick up voters between the two parties. And the hope is that first past the post winners in each local district represent all the voters in that district (e.g., local road repair, securing local school funding, etc.).
But with proportional representation (and other voting systems too), you get the kind of factionalism that exists in France and Italy. Without a two-party system, you need to cobble together governmental coalitions among various parties. You also need to circumscribe various communities into one representative pool, then have a collection of representatives for that pool as a whole, not for the individual communities.
First-past-the-post might not be the best system. It just isn't clear that other systems like proportional representation are better.