When talking about voting practices, he made the comment that he always straight-party votes, because that (paraphrasing) "is the only way anything gets done". That struck me as odd, since personal experience has taught me that cooperation is the only real way to accomplish anything in a group.
Sure, but making a majority of the group cooperative is easier if they are one party. Parties are incented to work together within the party, but there is less of a desire to work with the other party.
The biggest cause of partisanship in the United States is not straight-party voting but the primary system.
In the general election of a two party system, both parties will tend to become more like the other. This is because if you assume that voters pick the candidate that is closest to them, there is no advantage to being away from the median policy.
In primaries, that reverses. Primaries are dominated by the people who really care, which tend to be the extremes (conservatives and liberals) rather than the moderates. Until a party has been out of power for a while, it's hard for moderate candidates to get through a primary. So primaries not infrequently create two extremist candidates. They may move toward the middle during the general election, but it can be hard to drop a policy that a candidate avidly supported during the primary.
Plurality or first-past-the-post voting causes partisanship in primaries. Even in areas where the moderates dominate, if there are two moderates and one more extreme candidate, the more extreme candidate can win with the largest minority (plurality).
Another issue is the way that people have been self-sorting politically. People who like Democratic policies are increasingly located in cities while Republicans are in rural areas. Some of that has been the policies shifting, but some has been people moving. This creates more and more situations where the primary is the important election. But often the other party can't participate in the primary.
Eliminating primaries and moving towards a ranked system might help with this. Because it would empower minority viewpoints like moderation. But it would also reduce the power of the existing extremists. Which makes it hard to get passed, as the people who would most support it are those who end up unrepresented in the current system.