People coming to FI need to recognize they are learning about different ideas and dealing with people who don’t share all their assumptions, culture, and expectations. They must therefore be patient and tolerant. They must expect clashes, misunderstandings, conflict, disagreement, and problems. They must have some strength and tolerance to deal with the Other, to challenge themselves, to move past some minor quibbles, to discuss instead of give up when faced with some major conflict, etc.
People who find FI too mean are simply intolerant of people with a different style than them. They are expecting all discussion of bold new ideas to follow their existing ideas about what patterns of discussion are acceptable or unacceptable. But FI proposes that criticism is crucial to learning, and a helpful gift, rather than mean. If people want to deal with something which is grand, special and different, they can’t also expect it to perfectly fit into their existing life with little effort to understand a different world than what they're used to.
People also need to use judgement. FI discussion isn't a guided tour of the key ideas. Not every reply you receive, from every participant, will be great. It's an open place where anyone can join and talk without gatekeepers trying to decide who is worthy. That lets you in the door and it also lets others who aren't all amazing thinkers or even, necessarily, kind people. So what? Judge which responses have value and respond productively to those. Guide your own discussion by having some goals in mind and pursuing them, rather than getting distracted by whatever happens to come up and offended or disappointed that your aimless discussion hasn't achieved a great aim. And if you don't know how to guide your own activities, or what some good goals would be, ask. If you aren't even willing to talk about problems and ask for help, then you should expect to fail.
Making requests is a good strategy. If you want something, ask for it instead of expecting it by default. Do you want replies to you to be written in a particular style you consider "nice", and not to include some types of statements you find "mean"? Tell us what you want instead of expecting us to read your mind. If you can't figure out and write down what you consider nice or mean, you can't very well expect us to accurately guess it. You are used to dealing with people very similar to you in a tiny social circle who have lots of the same poorly-considered assumptions about life that you do. If you want to be exposed to the broader world, you'll have to think about and communicate your ideas more instead of just taking them for granted.
If you think something's mean, instead of getting offended, quote it and say what you think the problem is. You could be right. Perhaps the author could learn from you. Don't assume they are doing it on purpose out of malice. Ignorance and error are common. And misunderstandings are common. Maybe they were trying to say something else that's different than your interpretation. Maybe they'll apologize, admit they were in a bad mood, and try to do better. Maybe they'll point out and challenge some of your philosophical assumptions that you didn't think about. Find out what happens when you discuss a problem instead of thinking your conclusions (e.g. that something is mean and bad) go without saying.