I would say it's a bit more complicated than that. Many English speakers I come into contact with aren't actually English, they may be from just about anywhere. English is just the language that (I dare to say) most people on the internet understand and use to communicate with others from different nationalities. So these people are English speakers from a whole lot of different countries, including Dutch.

My guess would be that on the internet, you have much more control over which people you interact with, who you talk to, who you share your ideas and opinions with etc, generally leading to less conflicting conversations and less immediate feedback of disapproval (e.g. weird looks). Outside the internet we still have control over who we interact with, but definitely not always (think school, which has a major influence on our personal development).

Perhaps because of this (being criticized less online, generally more offline/face to face) and because the language I use on the internet is English while the language I use in daily life is Dutch, I've come to feel much more at ease when speaking English. This is just my personal experience though, I bet it's completely different for other people! And of course there could be plenty of other reasons for it, like maybe the language itself, but I believe this (maybe we could even call it subtle "conditioning") might be a big factor too. However I do wonder if there are others who can relate with this in particular.