I don't think it's looking at evolution as a negative thing, it's just that having the feeling that a band is going to change leaves the possibility of it sucking. There is favorable evolution and there is unfavorable evolution, the latter being what is looked at as negative. And it seems like when bands sound pretty much the same as on the previous album(s), it is more or less viewed as a good thing because it's better than taking that "chance" of evolution and failing.

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