I think there are three groups of people:
1) Short sellers. Short selling, as opposed to simply investing in a stock, is something that requires significant resources to begin with. Take these people with resources and acumen, and now given them a multi billion dollar incentive to see Tesla fail. You create a major motivator for people to not only speak negatively but to do all they can to try to foster and drive negative sentiment towards the company and Musk. This group of people are the main reason Musk has a problem with short sellers. Shorting is not bad, but the twisted incentive structure created by substantial shorting is. This group is made doubly effective by the fact that Tesla has chosen to keep with the strategy of a $0 marketing budget.
2) Useful idiots or trolls who simply enjoy attacking people without much of any consideration for facts or data. These individuals are already ubiquitous on the internet and unknowingly work as tools for #1.
3) People who genuinely feel Tesla is not headed in the right direction and would do better with different leadership.
---
In my opinion, the largest group by far is #2 followed by #1, distantly followed by #3. The problem is that #2 is a really really big group. They almost certainly already outnumber, by far, the entire population of people that go out of their way to speak positively of Tesla. So you end up with a perceived mass negative sentiment, even when in reality it's not really supported at all. E.g. - recently there was a motion to find a different CEO and it was voted down by an 83.5% margin. Another issue here is that Musk has decided to point out the awful behavior the media, which has also turned them against him. For instance on that vote I mentioned, reuters instead of reporting the result chose to run an article, "BlackRock voted to replace Tesla's Musk with independent chairman" with the numbers given, without percentages, in the article body. [1]
[1] - https://www.reuters.com/article/us-tesla-musk-blackrock/blac...