The VERY IMPORTANT OPINIONS
I believe it was Robert Green Ingersoll who put it best when it comes to art and morality:
In other words it means that if when the message we want to convey overrides the webcomic itself it ruins the overall product. It is normal to have something to say and want to express it through our art, but the problem is that with a number of webcomics, especally with those with political undertones (like Better Days and Sore Thumbs) is that the author's ideals and opinions override what should be the most important part of the story: plot and characters.
As Mr. Ingersoll said, this is one of the biggest problems with message heavy webcomics like the ones I mentioned. They are so wrapped up in their truth that they can't relate to those that don't entirely share their opinions. Take Sore Thumbs: the republican brother is such a right-wing uber sterotype that he finds no problem with killing people with beards because they "look like terrorists" and wishes to play video games naked with George W. Bush that he's an unrealtable and unlikeable sterotype. Same goes for the right-wing Better Days (to a different extent) where the author's dislike toward liberals makes him unable to see them as anything other than strawmen and scapegoats that can't be seen as people. Granted that I have come across my share of pundits that are pretty much cartoon characters in their own right, as a writer you have to remember that your characters are people first and their political\social affiliation second.
Same goes for the "voice of reason" that represents the author's own views. Because that character is almost never wrong, it makes them come off as lecturers and somewhat self-rightous. Let's put it this way, a story and a lecture are two different things, don't confuse them. To help you along, I suggest (especally for those of you who want to do right vs left stuff) something that got it right: All in the Family. While Norman Lear (the creator) did have a liberal slant, he made Archie Bunker (the right-wing character) a likeable human being that was more than his politics and was able to put them aside when things mattered most and maybe even learn a little something from time to time. As well as giving Mike (the liberal son-in-law) flaws and moments where his beliefs were made fun of, ugly moments and times where he was forced to question his own beliefs. When it handled touchy subjects, it remembered to put the story and the characterization first to help avoid it from being a lecture. On a sidenote, I also suggest Family Ties as well.
I hope this page will help you along and keep writing.