Tourism need not necessarily mean environmental degradation in many cases. I will cite of my personal examples related to this. In Maharastra, we have the magnificent Ajanta and Ellora caves which I have visited a few years ago. The government of Maharashtra does not allow diesel/petrol vehicles anywhere near the caves. All tourists have to park their vehicles some 15 kms away and board CNG fueled buses that are operated by the Govt. to get to the caves. There is a strict ban on use of plastic. Tourists are not allowed to carry food items etc to the caves. All of this has ensured that the places is kept clean and environmental taken care of.
On the flip side, I have visited Kedarnath in Uttarakhand a few times. On my first visit, I was shell shocked at what I saw. To get to Kedarnath, one has to trek 14 Kms from a small village called Gaurikund which was nothing more than a few homes and many shanties. The trekking path is 20 feet wide mountainous terrain. There are about 2000 kacchars ( donkey like animals) used to ferry people up and down the mountain that use the same path people use. Imagine these animals pooping and pissing on the entire path up the mountains. Tourists have to walk on this animal poop and the stench is unbearable.
The river Mandakini which originates in Kedarnath is a tiny stream at the top of the mountain where it originates and runs its course along the trekking path. Tourists dump all their used water bottles in this stream which is washed downstream and gets collected at a flat area near GauriKund. You can see thousands of plastic bottles floating on the water. In fact, you cannot see any water here but just bottles and garbage. Lastly, once you get to the kedarnath mountain, a small 20 feet wide road leads to the main temple. There are small hotels on either side of this road. The hotel have no drainage facility and they end up washing all their utensils in front of the hotel entrance on the road. The road is littered with leftover food debris dumped by these hotel. Can you imagine that?
I was so shocked at seeing the filth that it left me wondering how on earth can any Hindu pilgrimage be so dirty. I had never seen anything like that before in any hindu temple. Absolute filth! When I was there, the DM of the place was also visiting GauriKund. I remember stopping him at his hotel and pointing out to the gross negligence only to be politely pushed back by his secretary.
One-two day after I left Kedarnath, there was a massive cloudburst and everything was washed away in the floods. Apart from the sadness due to loss of human life and property, I was happy in a way that all that filth was swept away by nature. That place needed a reset badly and it came with a bang.
So, yes you are right. Tourism and environmental conservation has to go hand in hand. But its not difficult at all. It can done if our govt has the will to do it.
Edit: Eco tourism is actually more rewarding as people do not mind paying a premium as compared to normal tourism. All the more reason why India and its citizens should lay more emphasis on it.
Sorry about the long post