What adsbexchange, flightradar & co. are doing is almost certainly illegal in Europe under the GDPR.
This isn't exactly "public flight data", in many cases it's illegally collected and published flight data.
E: I can't reply to "imnotjames" below thanks to HN ratelimits, but here you go:
It's an obvious GDPR violation, just like it'd be an obvious GDPR violation to publish a similar database but with phone IMEIs and associated locations instead of aircraft.
This isn't exactly "public flight data", in many cases it's illegally collected and published flight data.
E: I can't reply to "imnotjames" below thanks to HN ratelimits, but here you go:
It's an obvious GDPR violation, just like it'd be an obvious GDPR violation to publish a similar database but with phone IMEIs and associated locations instead of aircraft.