The two comparable races are the 'half' races: Half-Orcs and Half-Elves. Why play one rather than the other? We'll look like that in a moment but first a repeat about what I said about Half-Elves this time as applied to Half-Orcs?
Not Really Alienated
Like for Half-Elves, I really think the Rulebook is referrring to an earlier time when Half-Orcs were not so numerous. After several generations Half-Orcs would have had time to create their own societies where they were the majority and individual Half-Orcs would no longer feel like outsiders. I tend to be keen on the kind of towns and cities Half-Orcs would build since they would most likely be an amalgam of the toughness of Orcs and the civilization of Humans - fascinating places showcasing the best of both worlds.
Half-Orcs vs. Half-Elves
Why play a Half-Orc rather than a Half-Elf? Because Half-Orcs are hated, specially by Dwarves and Elves. It can be fun to play a character that is pre-judged and disliked. If you've always wanted to be the outsider, the perceived 'bad guy' of the party, here's you're chance. You're Half-Orc isn't really a bad guy just misunderstood. Or, maybe he really is the black horse of the party. Fun right? It's time to misbehave in Golarion.
Half-Orcs vs. Humans
Think of a Half-Orc as a Human only bigger, stronger and tougher. This would be a beautiful match with the Barbarian class or the Fighter class. Racially, your PC gets a +2 on intimidate. Even better, a Half-Orc can still fight at 0 hp!
Just like Humans, Half-Orcs get to choose the ability to put a +2 on - an indicator that all the classes are open to this Race.