I think Rossi at the TT is fantastic. I don't think it is about whether or not he deserves to be there, but more about what his attendance can do to help the TT. Questions have been asked about how this could possibly benefit the TT, and, perhaps more importantly, the average racer, but I think it stands more chance of helping than harming both.
With the number of visitors to the TT steadily decreasing over the last 10 years or so, so the income to the Island from the TT has also reduced, meaning a reluctance to spend more on things to benefit racers, such as start money, ferry costs etc. The only way the Manx Government will be persuaded to spend more money helping the racers is if visitor numbers and therefore income increases.
Rossi has a lot of fans, who may not be fully aware of the TT or roadracing and never attended. If some of these fans are made aware of the TT by Rossi's attendance, they may be interested to find out more and attend themselves. You may say that this is rubbish, but it is the case that many Rossi fans now follow rallying purely because they have been introduced to it by following Rossi.
There is a Rossi fan page on Facebook, where it is advertised that Rossi will be attending the TT. This fan page, last time I looked, had about 1.3 million fans. That means in just one post on Facebook, the TT has been advertised to 1.3 million people.
I believe this can only have a positive effect on the TT, getting the TT out to a wider audience and hopefully, along with other things like better TV coverage, start increasing visitor numbers and generating more income for the Island. Then the Manx Government are more likely to be persuaded to give more help to the riders.