YABVU. While there are undoubtedly some reckless and inconsiderate bikers, they tend not to stay alive and able-bodied for too long.
I don't ride myself, but have ridden pillion for most of my life (I was 4 the first time I went on the back of my late father's bike, which probably isn't even legal now). I'm very bike aware.
DP has been riding for 41 years, and has been (touch wood) accident-free for 36 of them, including doing hundreds of miles a week as a despatch rider for 13 years. Apart from a few spills in his first year, his only accident was caused by a driver hitting him changing lanes without looking (dislocated hip, 4 months in hospital, in traction). He's managed this because he seems to have developed some strange kind of ESP that tells him when a driver is likely to pull out of a side turning, switch lanes without checking their mirrors or swerve because they're texting/eating/lighting a fag/putting their lippy on.
We ride a huge Pan-European with a big fairing, two very bright DRLs and a loud exhaust, and we wear hi-vis clothing and helmets. Still drivers fail to notice us, requiring some deft manouvering of a bike that weighs a third of a tonne (and that's before we've put 4 bags of shopping in the panniers). The carelessness of the average driver, and lack of observation, never ceases to amaze me. Even if they don't see us, they should be able to hear us, ffs.
I wonder if all the reckless riding the OP seems to encounter is done by bikers desperate to get as far away as possible, for their own protection.
Pleased to see that so many horse riders find bikers considerate. We always pass horses very wide and at very low revs, and we invariably get a cheery wave of thanks, so thank you for your nice road manners.