Oh, sorry, Coppice, I didn't realise it was
your sport
Back to the OP though - others have already mentioned social media, forums like this and stuff on the Internet generally, but speaking from a very personal perspective it's the immediacy that's killing everything with negativity.
Time was you had to wait for your preferred Thursday publication to come along to catch up on what happened last weekend, and along with it came reasoned and in-depth analysis and additional background context that you could then sit in the pub and argue about/discuss with your friends.
Nowadays, we can all voice an opinion on any subject (whether we're familiar with it or not) immediately, wherever we are in the world. The context is usually missing, the reasons for whatever we're opining on aren't necessarily there, and it's usually easier to moan than it is to congratulate or whoop'n'holler with joy.
Along with the immediacy is polarity: if you're not with me, you're against me. Thankfully, most of the time, Tenths is a fairly nuanced place without a great deal of blinkered bias - although not always! - and it is possible to hold multiple viewpoints here without being slagged off endlessly. It's an island of nuanced, non-polarised calm in a sea of murky polarity
To me, the word "whiner" sits alongside "fanboy". It's a word that's used as a stick to beat people, and it shouldn't be.