I cringe whenever I see Christians do dumb things (like claiming Jesus and/or Mary appeared on their morning toast and apparently pay for totally misguided billboards). And I can barely stand to see Fred Phelps' name or the name of his "church" mentioned on the news. (If you don't know who that is, you don't wanna know.)
So why does it seem like Christians so often do dumb things?
One reason is that when a Christian does something dumb, they're often identified (in the media or colloquially) as being a Christian, but when an atheist does something dumb, they're usually not identified as an atheist. Now certainly some Christians do dumb things in an attempt to follow their faith, but whether what the person has done is consistent with the Christian faith is often ignored.
A second reason is the fact that there's a lot of Christians around. Millions in Canada alone, plus many millions more in the USA, and approximately 2.1billion in total according to Adherents.com. So you'd figure, out of all those people, if even 1% do dumb things, that it will seem like quite a lot of people. Of course, the actions of a few don't necessarily reflect those of the whole. (See: Fallacy of composition.)
A final reason, extrapolated from the previous one, is that some Christians are dumb. (You're free to make your own evaluation of me if you'd like.) In fact before I was a Christian I thought all Christians were dumb, or ugly, or both. (I thank Greg Koukl for putting into words so eloquently how I felt at the time.) Dumb because they were roped into a false waste of time, and/or ugly because they had to go to church to be accepted, since it's the only place that people have to accept them.
And yes, many Christians are dumb (and/or ugly). But so what? So are many atheists, agnostics, and adherents of other faiths.
There are also many smart Christians … not myself, necessarily, but guys like William Lane Craig, Alvin Plantinga, Alister McGrath, John Warwick Montgomery, Timothy Keller, John Lennox, and Dallas Willard to name a few. So whether any one of them is smart or dumb proves nothing about the truth or falsity of the faith.
If you currently have the opinion that Christians are dumb, or ugly, or both, like I used to, I invite you to investigate some of the sites linked above or in the sidebar to the right. I think Christianity is worth thinking about, even if its adherents sometimes do and exceedingly poor job of reflecting it.
And if you are a Christian, let's try to reflect our Lord, Jesus, who as Dallas Willard describes, was and is the smartest man who ever lived (and lives).