There are a few reasons why people believe that Taylor Swift uses a voice tuner. First, her voice is often very consistent and smooth, even when she is singing high notes. This could be a sign that she is using a voice tuner to correct any pitch imperfections. Second, Taylor Swift has said in interviews that she is not a "natural singer." This could mean that she feels the need to use a voice tuner to help her sound better.
On the other hand, there are also some reasons why people believe that Taylor Swift does not use a voice tuner. First, her voice has a lot of natural character and personality. This is something that can be lost if a voice tuner is used. Second, Taylor Swift has not explicitly said that she uses a voice tuner. If she did, it is likely that she would be criticized for using artificial tools to enhance her voice.
Ultimately, it is up to each individual to decide whether or not they believe that Taylor Swift uses a voice tuner. There is no clear evidence either way, so it is a matter of personal opinion.