[fjtorres]

Yes, visibility matters.
Marketting and promotion is a feedback loop after all. Heavily-promoted stuff sells.
Likewise, people's judgments are molded by the information they can get their hands on even if the information itself is flawed/skewed/misinterpretted. "Truth" is what you are told is true. (Big lie theory and all that.)

Examples abound: every week we see media reports of medical studies linking a specific food type/behavior pattern to a specific medical condition, yet rarely do the reports bother to remind people that statistical correlation does not imply, much less prove causation. Instead, we see people running around in a panic to rid their household of the "tainted" items.

Quality of data that gets broadly reported is rarely addressed, especially if doing so gets in the way of a good headline. One example that comes to mind is the "awful" infant mortality numbers in the US, as compared to other UN published numbers. Lost in the fine print is that different countries use different criteria in compiling their data and some define "live births" as any infant still alive after 48 hours while the US tallies premies and other infants that elsewhere are classed as stillbirths. (And never mind factoring in context that might explain what the numbers really mean.) Mark Twain's "Lies, Damed Lies, and Statistics" comes to mind.

The movie industry is getting itself in trouble that way. In their haste to hype intended blockbusters to maximize up-front revenue they are creating an environment where any movie that fails to rack up enormous numbers (for whatever reason) is instantly branded a failure and all marketting ceases, thereby ensuring that the masses bypass it and that it does in fact fail. Unlike previous decades where movies were allowed to find their audiences with sneak previews or just waiting for word of mouth to let attendance grow over time, the studio beancounters essentially give up after one week. It's as if they are putting out movies that they themselves don't understand or believe in.

So, I guess the question about pessimistic SF really comes down to why is the pessimisstic stuff more visible?

I already presented my thesis: times suck so the negative stuff resonates better with those readers not actively looking for escapist entertainment. It's cyclical.
Wait a year or ten (or until the Hunger Games Frenzy dies out) and we'll be up to our gills in bright sunny narratives.