I agree to the point that negative posts like this can affect a person's motivation to do something such as modding however this is also a reality of the internet. It is not a phenomenon specific to modding but just the nature of the internet.
You will find people hating on a artist or a genre of music, a brand, a politician, a diet, etc. Each person is unique in their own way which is also why not every person will agree with one another because we all have our own way of doing things. Add the fact that the internet is like an open forum where anyone can just say/post what ever they want, people will take this opportunity to express their thoughts on the thing that they love and hate.
All we can really do is send all the love and support to the people that we care about, in this case our modders, to drown all the negativity other people direct at them and encourage them with praise, constructive criticism and support.
Edit:
And also ignore the trolls since they just thrive on getting you to react how they want you to react.
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Will there be enough Dakka?