The over use of "Bigot", "Racist", "Nazi", etc completely devalue the words. They take away their power. 10 years ago nobody wanted to be called a Nazi but now people laugh it off. That's dangerous. We want to be be afraid of being called a racist. We want to discourage it.
When Suzy soccer mom says she wants some stricter vetting for refugees she's not the same as Billy Bob sitting in his cabin planning out the burning of black churches. But the left has gone full throttle in that direction. They take the easy path of calling someone a name rather than defend their position, even if it's perfectly defensible.
These loud voices are drowning out the moderate, reasonable people on the left, and pushing them away. This is a bad long term strategy.