As Christopher Caldwell once observed in the Weekly Standard, Darwin fish flout the agreed-on etiquette of identity politics. "Namely: It's acceptable to assert identity and abhorrent to attack it.Goldberg is quoting Caldwell, but presumably is supporting the statement. There is a lot here to rebut and discuss. First, in two-way communication through symbols and symbology: the person displaying the symbol gets to decide what the displayer means by the symbol. And there is the reverse: the viewer gets to decide what the viewer thinks of the symbol.
Now, asking someone what their symbol means does not necessarily get you what they really mean. We've all heard "its just a joke" and "my comments were taken out of context" ad nauseam as excuses for stupid and offense comments, from politicians and from our neighbor's children, not necessarily respectively.
People who display the Christian fish symbol as a statement about their religion, separately from their belief about biology I would not mind if I knew that to be the case. But to me (how about to you?) the Christian fish symbol is used to indicate a disbelief in science and specifically biology. This takes the fish statement away from the realm of religion and into the realm of science.
To scientists - religious or not - and to scientifically literate people of any stripe, denying evolution is a bit like denying that you have freckles or a cleft chin. Evolution is a statement of fact, not of belief. Evolution can be checked. It is not up to you to believe it or not believe it. Scientists 'believe' evolution because it describes the world that we see around us. If evolution and the various detailed descriptions of our world did not describe the world, if evolution did not make predictions which are shown to be true, then scientists wouldn't 'believe' in evolution.
Believe is the wrong word, but I'm having trouble thinking of a better word. Other possibilities: 'Follow', or 'act as if it is true', or 'act as if it is true until something better comes along' are competitors. Definitely the word believe for the religious person and for the scientist are not the same activities.
Consider two parallel hypothetical experiments. Suppose that all knowledge about evolution and biology were wiped away. Would humans reinvent the concept of evolution? The answer is almost certainly yes. Now consider a second hypothetical experiment. Suppose that all knowledge of Christianity were wiped away. Would humans reinvent it? The answer is almost certainly no. We haven't tried the first experiment, but science does attempt to operate that way: there are a lot of brownie points in science for someone who can disprove a widely held belief and replace it with a new set of facts. We have essentially done the second experiment. Christianity spreads by people having babies and by teaching others about it. It doesn't get reinvented from scratch. Humans have invented lots of other sorts of religions when given the chance, but not Christianity.
In science there is no controversy about whether evolution is true or not. Evolution happens. There are a lot of details to evolution: evolution isn't a simple little mathematical result like e equals m times c-squared. These details need to be worked out, and we do not know all the details. There is a lot going on, and scientists are very busy working out details and elaborating how evolution works. There is much work to be done in elucidating how much evolution goes on, how evolution proceeds, whether there is a better word to describe what we observe in nature, can we use evolution to our own ends to make better drugs or chemicals or products, who should get credit for what discoveries, and so on, the business of science is quite extensive.
Displaying the Darwin fish symbol may indeed be a statement about me, but for Darwin fish displayers, the Darwin fish is more importantly a statement about the world. And it is a checkable statement.