great question. i am certain in most cases positives would outweigh negatives. as the saying goes all advertisement is good advertisement. one example is car sales from cars that appear on top gear all increase regardless of the review the team give.
one thing that does put me off buying supporter gear is not the sponsor itself, rather the size of the logo, for example football jumpers with a huge logo planted on the front is not something you want to wear.
in Australian Rules Football the logo of the company on the front of the jumper is heavily restricted in size, always rather small, always in the same location, and always the same size.
therefore regardless of the sponsor supporters love the jumper for what is has always been for 100 years, not half of the jumper space advertisement