The threat is real and ignoring it will not make it go away.
Lisbon and Casa aren't situated in the Ruhr valley thus are poor comparisons. Almost as poor as comparing Dubai to other large western cities. In Dubai non-asian expats stand out from the crowds and congregate in a relatively small number of predictable areas. If non-muslims are targetted here you will soon feel very vulnerable with few places to hide.
Have a nice day!