Maybe they've been reading Marx more closely than you:
The social division of labour goes to the heart of Marx's critique of capitalism.
And so the division of Labour that existed in the Paris commune between those who were elected to organise and the rest, that Marx supported and was to inspire his life's work?
I don't think destruction of the structures that compel a division of Labour on class grounds, capitalism, negate a division of Labour for Marx. For me the difference is, the product of the division of Labour is held in common, and the process of the division of Labour is held in common, by producing democratic structures that negate the power of the expert, manager, or anyone.
So those in the Paris commune who held the 'power' to lead and organise, had that 'power' negated by the fact they were paid the average wage, electable and sackable. They don't have power, because they are controlled by the common.
To deal with your specific point, That ie Stephen Hawkings would be free to fish, to hunt etc, does not mean he would be compelled to be distracted from his expertise. This would be ridiculous. However exploitation of the many through the use of his expertise would be negated by holding in common the product of his expertise.
The notion that you can abolish, or even deny expertise is illogical. That violent panda is more expert, is more advanced in the appreciation of social change, in the knowledge of how to achieve it, than a BNP member, is obvious to me. Is it not obvious to you?
So for me the activist's are often NOT mistaken to believe "The activist is a specialist or an expert in social change. To think of yourself as being an activist means to think of yourself as being somehow privileged or more advanced than others in your appreciation of the need for social change, in the knowledge of how to achieve it and as leading or being in the forefront of the practical struggle to create this change." They often are more expert. Where they are mistaken is to believe that they can substitute for the working class, bring about social change on behalf of the working class. The emancipation of the working class, has to be the act of the working class, because until they know how to take power, they cannot know how to hold it in common and so negate it.
The only caveat I would add to that, is that the expert/teacher who forgets how to learn, is no longer a teacher/expert. The situation between a activist, and the working class is dynamic. As the experience of the Russian Revolution shows. Often the working class can be in advance of the activist. Even if you are not part of the class, as in the case of Marx and Engels, you have to be organically connected to the class, to achieve social change, social revolution.
[BTW violent Panda, I believe this last paragraph negates your argument about the socialist workers party not being part of the class. Though I don't necessarily accept your argument, the constituency of the SWP is not working class. We don't have the evidence to say one way or the other. I can only work off my own experience, and that says the vast majority of them were.]