Us vs them mentality. If the goal of islam is to convert the world to islam. Then there are two sides, the believers and the non-believers. The believers know it's right and will be rewarded in the after life. The non-believers don't know what's right or they do and are trying to stop islam from succeeding. Either way they are treated as a threat that either needs to be controlled or eliminated.
As we all know being offended in religion is like yelling, "He hit me first", in a school yard fight you started so you could beat the other person up. It is just a way for them to validate their actions. It's a standard psychological behavior for people with inferiority complexes.
Here are two excerpts about psychological validation that should explain it quite well:
Low Tolerance-Due to one being validated by others, one is likely to have a low tolerance to being invalidated. Being around people that honour who they are and what they are going through is not only part of their life experience, it is also what they have come to expect from life.
Invalidation -To the person that is invalidated, the world rarely mirrors back their true reflection what this person sees does not create happiness or joy; what it creates is frustration, anger and a whole myriad of other experiences. This person is also likely to have a high tolerance for being invalidated. And how this invalidation is experienced can range from being ignored and unacknowledged to being physically or emotionally abused; with abuse being the extreme version of invalidation. Either way, each form of invalidation carries its own form of pain and suffering.