Whatever the reason may be, printing text messages is possible using your iPhone, (and most other smart phones). There are two methods to print text messages.
The first method is to copy and paste each block of text and paste it into an email on the phone and then send that to yourself. To copy text, use your finger and hold down on the block of text you wish to print. Select copy. Go to the blank email, tap and select paste. This method is great for printing specific portions a of text message. However, longer text messages are more cumbersome to print this way.
Another method is to take a snap shot of the text. Line up the text message, either from the very beginning or from a desired starting point, and hold the on/off button and home button at the same time. A snap shot is taken of the screen, (which is the text message). Move the message to the next section and repeat the process until you have taken a snap shot of the entire message or have the desired text captured. Go to your Photos app and print each snap shot just taken.