…simply by giving them attention.
Time and attention are the only two things that are really scarce on our planet. Each one of us only has 24 hours in a given day, and most of those hours are already dedicated to certain things (like sleep, eating, working, etc). Your “personal discretionary time”–the time you can allot to anything–is really a very small amount. What you spend that time on indicates what you value. When you take time away from something of greater importance (e.g. eating or sleeping) then it shows a great amount of value, indeed.
You can spend that time in one of two ways: on things that you think are positively important to promote, and on things you think are negative and which you think are important to stop.
Either way, by giving things notice–by spending time on them, talking about them, linking to them, pointing them out–you are indicating that those things are important. Because you spend time on them, others (whom you influence) might spend time on them too.
Many things which seem to be bad are things which will not endure in the long run. By giving them attention, you may actually be helping them to endure. Some negative things would die out quickly if they simply didn’t have a lot of attention.
Before considering whether to give something your time and attention–and influencing others to do the same–consider whether this thing will be “yesterday’s news” tomorrow and forgotten the day after that. Simply denying attention to bad fads may be enough to starve them of the oxygen they need to survive.
On the other hand, things which are truly evil need to be given much focus, indeed. Here’s a recent Albert Einstein quote I ran across: “The world is a dangerous place to live; not because of the people who are evil, but because of the people who don’t do anything about it.” God give us the insight and boldness to focus on the things that truly matter.