When someone contradicts himself, it seems to indicate that he does not believe what he is saying and thus paid little mind to the arguments he has made, that he does not understand the situation at all and is merely speaking to feel productive, or that he is simply lying and has been caught in this deception. If any of these situations prove to be the case, the immorality of contradiction is rather obvious. In order to explain, allow me to address each situation separately.
In the first, the immorality is in the man’s willingness to engage his neighbor in an argument in which he has no real interest. To debate something because you feel passionate about it is admirable, while to argue an issue of which you have no concern makes you appear a rather spiteful and unkind person.
For the second, immorality can be applied to the idea of involving yourself in an argument in which you have no understanding. In this situation, your need to be heard implies that you are desperate for attention and lack self-worth enough to be secure in your knowledge or lack thereof. The attempt to valid yourself by becoming involved in a discussion of which you know nothing does nothing to encourage people to think highly of you: in fact, the exact opposite. It is likely to cause people to think less of you and to avoid situations where you might be able to make a greater fool of yourself.
The final scenario presented is the most obvious. Immorality abounds when you intentionally mislead another.
I believe these examples make it rather easy to determine a correct moral code in regards to contradiction and its avoidance: always avoid lying, and if you do not have the necessary intelligence or passion for the argument, excuse yourself from it.