In some cases that may be true but I don't think it's true in general. So what's the deal here?
I suspect it's because the criticisms are often vague name calling and hand waving. Rarely do you ever see specific issues articulated. Just a lot of juvenile absurdities such as he's a Marxist or a Muslim or he hates America. So the problem is if you can't take the criticisms seriously, what's left to explain the venom?
For what's it's worth, here's my opinion of the situation. Many people in the US feel like they are losing control of their country and that the US is losing its ability to influence what's happening in the world. Of course, they're right.
The demographics of the US are changing rapidly. The economic power is shifting to China and generally evening out around the world. This is frightening a lot of people and there is some justification for that fear. Obama is the visible manifestation of these changes because they're happening on his watch so, subconsciously, they blame him for what's happening.
The fact that he's black, actually, he's HALF black, makes him an even more potent symbol of the changes especially to the change in US demographics. His policies haven't been terribly radical. You can disagree with any number of them, and I do by the way, but I don't see anything in policy disagreements that can explain the pure hatred many people seem to feel for this guy. It's just not justified based upon politics as usual.
Things seem to be going downhill and people figure it can't be their fault; it can't be the country's fault because they've been weaned on the fiction of American exceptionalism. But it must be someone's fault? So hey, Obama is as good a whipping boy as anyone.
You know, about losing the country, people said the same thing during the civil rights movement and the Vietnam War protests. And at least then we weren't also in the middle of scary economic changes as well.
It's a tough time. But it's always a tough time for some reason or other. In the 30s it was the Great Depression; in the 40's a little thing called World War II; in the 50s and early 60s the challenges to segregation, which brought enormous changes; in the late 60s the Vietnam War and in the 70s we had runaway inflation and a series of useless presidents. Now we have terrorism, lingering economic issues, including an ever increasing degree of income inequality and a ridiculous debt burden. Then of course there is the emergence of the Gay Rights movement.Tough and sort of scary times indeed. The country is definitely changing, but we got through all the other tough times and all the other changes and we'll get through these too IF we start to focus on the issues and problems. I don't believe we're doing that right now and that worries me more than anything else.