Home team/Away team
Seems like a lot of people on the boards don't understand what happens when a team from a visiting area plays against a team from a local area, where a large majority of the fans watching from the crowd are also from the local area.
The home team gets cheered for, the away team gets booed. It's literally called 'home field advantage'. It's part of being in a competitive league that plays in different regions. When the visiting team has a history of destroying the home team, that's usually reflected in how the fans cheer/jeer the teams. Expecting NA fans to be happy and giddy about watching their team get rekt by Korea and not cheer when NA makes a play is just ignorant. You can still appreciate the plays Korea makes and be upset about what it means for your team.
I seriously doubt that the foreign teams were caught off guard by the support for the NA teams in the literal middle of the USA.
The players are adults. They can take it. Especially if you want it to be considered a sport.
http://chaparral.info/wp-content/uploads/2012/08/Home-Team.001.png