There are 2 Oregons.
Portland and the Willamette Valley are where the majority of the population lives. This area tends to be extremely diverse, liberal, Democratic, and pro-Obama.
The Oregon coast, southern Oregon, and eastern Oregon are more rural, more working-class, almost exclusively white, and far more conservative. These areas resent the Willamette Valley for passing laws that impact the entire state.
Roseburg...where the shooting occurred...is a very conservative logging town. Most people there hunt, and the rate of gun ownership is about 100%. That area is also economically depressed and underserved by law enforcement. There is also a huge resentment against the Federal government because the Federal government owns a huge amount of land in the area and prevents logging on it, which creates a chronic shortage of tax revenues for local communities. Police response times in areas outlying Roseburg can be up to one hour, if at all. As a result, people rely upon themselves and their guns for protection in a way that might seem foreign to someone accustomed to city life. They don't appreciate a President who flies in from a thousand miles away and tries to blame gun ownership for a tragedy that happened in their community.
Obama was actually greeted quite warmly in Oregon. He had to land in Eugene, which is an uber-liberal college town full of Obama supporters, because it was the closest city to Roseburg with a runway big enough for Air Force One to land on. He then flew 90 miles south to Roseburg by helicopter, and pretty much landed in a totally different world.
I don't necessarily agree with disrespecting Obama, but I am from this state and I can understand their frustration with him in a way that you cannot.