When something this surprising and awful happens, you cannot help but doubt the people on the same side as he, especially in a case of religion. This gives the religion and all its members a really bad rep, and for the most part will always live in the minds of everyone. Yes, that will impede on the truthfulness.
Ted Haggard's impropriety is one reason why we need to question the honesty of all pastors, but in truth no one in a position of authority should be given total trust unless he or she has proven themselves. Abuses happen because people want to turn their lives over to those they want to think are perfect.
While Ted Haggards poor judgment should make room for question about all pastors, I don't understand why this is not apparant regardless of Ted Haggard. Sure he proves a point, that you can't trust someone for their title, but then we shouldn't judge anyone by their title. Just because one is a pastor does not make them any less human than the rest of us, so why would we expect anything more?
It probably shouldn't, but one pastor's / minister's misstep always makes people wonder about other pastors and ministers. "Are any of them honest?" is a very common question, both among believers and non-believers. Non-believers are skeptical to begin with, and how they get yet another proof that yes, all those preachers are crooks. And believers lose trust in someone they thought they could follow. That makes them question other preachers as well.
No, just because he has had a little trouble here in the recent past, does not mean that a lot of pastors here are telling a whole lot of lies all of the time. I think that most of the time they are just wanting to help out the people.