In an Internet forum like this, there is no thought of physical confrontation, no interruption, you can leave a conversation at any time, you don’t have to hear people’s voices or wait for them to stop talking, you can get in as many words as you want without having to wait for people to stop talking, you’re not forcing anyone to stop and spend their time listening to you when you type something here, they’re not a member of your actual physical community who may gossip or undermine you, the social norm is to discuss things at length in text (and in person it is generally not the social norm to have long conversations about sensitive subjects with strangers who disagree with you) etc etc.
So there are quite a few things that create openings for more interaction online. Quite a few reasons exist in in-person situations to not stand around arguing with people who disagree with you about sensitive subjects.
Oh, also, words said in person to a stranger about some disagreement generally get lost in the wind, barely if at all considered or remembered by others. Online, the whole community and people lurking and browsing years later may read what you wrote. So from one point of view, it’s a reason to voice your thoughts that doesn’t exist when it’s only some dude talking to you at the gym.