I agree that the problem is caused more by the tourists. I too think that the government should change the proposed route to avoid the main wild life areas. But I feel a railway is necessary to reduce the problems being caused by the road traffic.
Nothing is going to stop tourists from visiting the place. Within a span of 8 years, the number of tourists here, just from Bangalore alone, has increased many fold. And it's not going to reduce. More and more people are traveling here by cars, buses and tempo travelers.
So,...
more... whether or not the railway line is constructed, the tourist traffic will increase. In this context, the road vs rail argument should be addressed.
Consider the traffic through the Nagarhole national park. Everyday, there are hundreds of vehicles passing through this park by the highway. This causes a lot of disturbance to wildlife.
In the late 90's, there used to be little traffic in the region (Nagarhole, Bandipur and adjoining areas). Other than the wildlife centers, there used to be little to no human presence in the area. It was very common to see animals crossing the roads in the day time.
Now, there are roadside dhabas, settlements every few kilometers and for the most part, animals don't even dare to come near the roads in the day time. The human-animal conflict is also increasing now as animal movement is extremely restricted during the day time.
A railway line will help in reducing the road traffic, which is the main culprit in reducing forest cover ( More and more buildings are constructed beside the roads, leading to loss of forest cover) and causing harm to wildlife.
A single train running through the national park can replace hundreds of road vehicles. Instead of several hundred vehicles constantly passing through the forest, just two trains ( one in each direction) can do the job. This will have far lesser environmental impact (less disturbance to wildlife, lesser pollution) than the road traffic. Even in terms of goods traffic, a single goods trains can replace at least 50-60 lorries.
We cannot avoid tourists and freight traffic through this region. It will only increase. So, we just have to pick the option with the least impact possible, and a railway line will have extrmely small impact compared to roads and highways.