Why would any European airline fly over Belarus while the incident isn't resolved? No airline should fly over states which intercepts civil airliners in transit.
Yes, Russia, like any other state, could intercept airplanes too. But so far, they have not. International air travel means, that you have to fly across many countries, if you want to fly in a somewhat straight line. There are a few exceptions, where flights are not permitted to cross a countries airspace, but intercepting approved flights is pretty much unheard of. That is why the actions from Lukashenko created so much outrage. It is one of the fundamental agreements of international flights that got violated. If Russia would start intercepting airplanes, they would be internationally isolated quite quickly.
My understanding is that you can intercept a plane in transit in your airspace. The problem is that Belarus lied when they said they had information of a bomb onboard.
Another problem is the kidnapping of a passenger who then got promptly very sick and damaged in the friendly heavy hands of the KGB and police. You know, the usual thing the totalitarians do.
Eh, how is Assange doing? People are being treated well in Guantanamo? Didn't Austria divert a flight on merely the suspicion that Snowden might be onboard? Or does that not count because it was just the President of Bolivia's official government jet and not a Ryanair flight?
Fair enough if you want to criticize Russia for being a kleptocracy that assassinates enemies on foreign soil, but diversion of flights to capture enemies of the state and then not treating them well in captivity is unfortunately not a hallmark of totalitarian regimes but a general feature of western statecraft as well, so let's not blow this tit-for-tat response out of proportion.
How about, don't be so eager to rush to judgement of other nations, when your nation (UK/USA) clearly has extant history with the same kinds of issues.
Practically I view the fly over ban as protecting passengers and property from being unduly seized by Belarus.
Since Belarus and Russia have close ties flying a plane into Russia at all seems about the same risk as flying that plane over and into Belarus.