Yes, you do have the choice of whether to follow the advice or not, and he has the choice to refuse to be your doctor if you refuse to follow his advice. So you have the choice between following his advice and not having a doctor.
Also, watch this video, please:
You make it sound like there is one doctor out there. There are many. People often switch providers because of insurance reasons, personal preference, etc.
Some people do have health issues and avoiding meat may help them rebound for a few reasons. Sometimes there are a lot of omega 6's in commercialized meats. Avoiding excessive meat can cause an improper omega 6 to omega 3 ratio, which can cause health issues. Some people have gut absorption issues and they may not be able to digest food well. Steamed veggies, green juices, etc. can ease up the burden some people have of breaking down all of that fiber. Most people out there aren't getting as many veggies as they should. Veggies should fill half of our plate per some recommendations at meal time, but many meals don't include veggies at all.
Many modernized western diets go like this: A bowl of cereal for breakfast (usually a lot of carbs and sugar) with milk, a burger with fries, and then lasagna for dinner. High carb, low vegetable, and that alone causes problems. A lot of people are eating more carbs and meat than their bodies actually need and not giving their body enough vegetables. When people eat only vegetables, they are probably meeting that goal so they feel a whole lot better and they stick with it. It's true, in this country our consumption of meat is generally way more than our body will actually use. So these people are probably not imagining they feel better. However, I don't think this type of diet should be long term, the body does need protein as building blocks for many things like your skin, muscle contracting, blood clotting, etc. Vegans and vegetarians have been more creative about getting protein in their diet along with a lot of new products out there these days, but meat has an easier source of iron, zinc, and vitamin b12 that can be beneficial.
The Beyond Meat stills scares me - too much estrogen, grown in a lab, what can go wrong, right? Hopefully it's a market that won't last. Some meat impostors are created using a fungus, which some people can have fatal reactions to. It's not natural to grow meat, I stay away. I don't eat at restaurants that serve it because I don't want my meat replaced. Some places are guilty of making that mistake or running out of beef so they serve you the imitation instead.