> Why do people love to act like both parties are the same? Is it just errant, broad pessimism?
On the contrary, it's not necessarily pessimism, the people who feel that way are probably just rather focused on the issues where the candidates are depressingly similar. For example if you want to see military spending massively reduced, the financial system reformed in fundamental ways to reduce systemic risk, or massively increased gasoline taxes to cover infrastructure improvements or green energy development, you probably feel badly served by both parties and their candidates right now.
On the other hand, if you're a gay man who wants to get married and start a family, or a redneck who wants to be able to carry your .357 magnum wherever you want whenever you want, or a rich guy who wants to keep your taxes as close to zero as can be achieved under the current two party system, the party differences are rather more obvious to you.
It's not really a question of pessimism, just the way people prioritize things. A person who has a lot of strong interests in the first category of issues (where the parties are rather similar, or just similarly useless) might be a lot more likely to say the parties are the same than a person whose strong interests are in the other set of issues.