Whilst, needless to say, I am totally with you in terms of virtually everything you say about winston and his opinions, this one is a bit different.
We are potentially talking about Joe Public who, no matter how intelligent he/she may be in general, may well assume that if they find a 13A socket, they can plug into it anything which is powered via a 13A plug. I accept that, although even this would be very rare, it's therefore not impossible that a third party Joe P would plug a high-power load into a socket they found in a loft. The reason I consider 'the practice' to be reasonable (although not totally ideal) is that (a) as above, it's very unlikely that anyone would do that in the first place and (b) even if they did, the chances of anyone coming to harm as a result would be extremely low - probably less of a risk than crossing a road or driving a few miles.
Having said all this, for purely practical reasons (not considerations of 'good/bad practice'), I do try to avoid having the lighting (or anything else electrical) in a loft/roofspace powered from the lighting circuit of the floor below. Whilst that is obviously usually the most convenient way to 'find electricity' for such a place, one of the fairly common things one does in a roofspace is work on the lighting circuit of the floor below, which obviously has to be de-energised whist one does that work.
Kind Regards, John