Bus lanes are there for public transport - which is a social good - as it reduces pollution and congestion for a given volume of people. Cycles are allowed in for the same reason.
As are motorcycles. If you're in traffic, you are traffic - by the same token if you're happily whisking past traffic then you are not traffic. Motorcyles are often a superior solution to cycles, they take up a similarly small amount of space and have the same jam busting powers in town with far more useful range and speed outside of it.
Weird figures in the linked article:
New research published by Transport for London today found that the collision rate for cyclists using bus lanes increased 273 per cent.
Figures also show that, over a 10-month comparison period, the rate of motorbikers being in a collision in a bus lane increased 133 per cent.
But bizarrely the collisions were not between pedal cyclists and bikers - but between vehicles and bikers, and vehicles and cyclists.
So the motorcycles are making cyclists crash into cars? I doubt there's a causal link. Something like (for an example) introducing more (or even just one more) cycle lanes that run up the left hand side of traffic at busy junctions during that period could account for the increase in cyclist collisions. And the sample sizes these figures are taken from are too small for real statistics, cyclist collisions rose from 7 to 21, for example. That could be a single critical mass ride meeting one white van.
The only negative effect on cyclists from bikers sharing bus lanes is a diminished sense of privilege.