I like the Darwin fish. To me, it is a healthy pro-science statement. Of course, I acknowledge that it also carries an anti-religion connotation for some people due to its design (i.e., borrowing from the Christian design which came first) and the inevitable conflict between religion and science. I'm also aware that some people view displaying a Darwin fish as an act of symbolic aggression. More than just being an interesting symbol that is interpreted in diverse ways, the Darwin fish exposes the scope of Christian privilege and says volumes about the plight of nonbelievers.
I do not have a Darwin fish on my car, but I would very much like to. Why? I perceive it as one of the rare symbols which conveys both a pro-science and an anti-superstition sentiment simultaneously. Since I am both pro-science and anti-superstition, it is an unusually accurate symbol for my worldview. But the main reason I'd like to have one because of how it makes me feel when I see one on another vehicle. They are a rare sight around here, but when I glimpse one, it instantly puts a smile on my face. Suddenly I am no longer alone, even if only for a brief second on the road. I'd like to be able to spread that feeling to other freethinkers.
Isn't this the main reason why Christians put Jesus fish on their cars - they like how they feel when the see one on another car? I'd like to have the same option. If they have the right to be part of a Jesus fish community, communicating "I'm one of you" to other Christian drivers, I'd like to be able to do the same a nonbeliever.
I do not have a Darwin fish on my car because I am not interested in having my car vandalized. I have known a handful of people in the Mississippi community where I live who have had their vehicles vandalized for progressive symbols as mild as the official bumper stickers of Democratic presidential candidates, and I have heard conservative Christians talk about damaging vehicles for messages with which they disagreed. In other words, I have empirical evidence (e.g., reports of vandalism to vehicles displaying progressive symbols) to support my estimation of the likelihood of vandalism.
So while I have the right (in a legal sense) to display a Darwin fish, exercising it requires me to put my personal safety and my property in jeopardy. Christians do not have to worry about this when they affix a Jesus fish to their vehicles, put on a cross necklace, wear a Campus Crusade for Christ t-shirt, or engage in some other symbolic expression of their beliefs.