It's no more dangerous than any other 2-door coupe, as rear-seat passengers can still exit on the other side just like in any other 2-door coupe. Logically, then, there should never be any door on a side in which passengers might be struck by traffic. But, common sense being what it is, most people tend to look before stepping out.
The difference is that when in other situations, like in a car park or in your own driveway or in your garage, you now have better accessing options, particularly if you have kids to deal with. Easier to place a car seat back there, or belt up kids w/o car seats. Makes it easier for the driver in RHD markets to put packages in the back seat; no need to go to the rear if you don't feel like it.
The consensus in most reviews outside of Clarkson is that it offers much more practicality (better access, more cargo volume, can now seat 6-footers) while sacrificing little in driving fun. The blind spot is a legit concern though.

Anyone who's driven a Mini Cooper S (both the super and turbo charged variants) will appreciate the essence and spirit of the car.

The Clubman is nothing more than a dubious marketing effort. My comments posted elsewhere in Clubman threads remain. Whilst BMW's marketeers may be able to justify the raison d'etre behind the Clubman, the point remains - the Clubman has no real motoring merit over the Mini.

MINI Clubman awarded "Ugliest car of the year " 2007 by Top Gear.

I couldn't have said it any better. BMW isn't doing this for Mini heritage, they could give a rat's ass about that, they're doing this purely to sucker people into buying this by projecting a certain image. As nice a car as the Mini is, the clubman is just horrid.

Do some people really take it seriously what this guy says? Start hosting a real car proram, Clarkson...