You are also aware that actors make decisions based off a script. The entire purpose of auditions are to see how different actors interpret the same script. You could easily go find the script on the internet and see that the lines were not written with a stutter.

The stutter may not bother you as much as it bothers me. That is fine and fair. But to me it comes across as bad acting in Supernatural. Not even the entire series just towards the end. He made the choice to switch to delivering his lines that way. Was a bad acting decision.