The $20 sounds like a reasonable firewall for trolls. It's easier to ban you if you're trolling and have to pay $20 for an account. Kinda like GAF's paid email registration.
Paid membership will not stop trolls of any form. Something Awful's forums are a prime example of this.
Anyway, for those who think Nintendo's online service setup is strange, think of the primary demographics of the Switch in the domestic and international markets.
The domestic market (Japan) is full of mobage gamers who are increasingly unlikely to have a home console. Online multiplayer games on the 3DS were either played ad-hoc (Monster Hunter) or otherwise featured mostly canned communication options. Many online titles didn't even require any discrete communication between players.
The international market (the West, Asia, etc.) has more console saturation, as well as more people who are equipped with the necessary accessories (headsets, etc.) for online multiplayer. There are many more people who are used to services such as PSN/Xbox Live, as well as many people with smartphones, like Japan.
In short, Nintendo wishes to bridge the gap between smartphone-savvy Japanese Switch owners who may not be fully equipped for infrastructure online multiplayer, and Western players who are already ready for the experience. Nintendo is only as prepared as they feel they had to be, given their history with online multiplayer, and the pressure they faced to adopt its tenets.