May I offer my general view on this thread and the opposing arguments? My perspective on all this is from the point of view of a capitalist. I am a business owner. I employ people. So, why am I interested in socialism?
Well, my background is working class, and I was exposed to left-wing ideas and trade unionism in my formative years. So, I am a broad sympathiser with the socialist movement - admittedly, perhaps for emotional reasons partly, but I think mainly it's a rational position. Capitalism was once a progressive system, but it is now looking increasingly outdated and does not appear to provide a mechanism for resolving some of the most pressing issues facing us - such as mass starvation, possible nuclear annihilation and environmental sustainability. I was looking for some discussion and I happened on this thread. Coincidences happen.
If my employees started asking me for higher wages and threatened to go on strike, I would be worried. But I would only be worried within the framework of capitalism, if that makes any sense, within the context of the social relationship of employer and employee. OK, if I can't afford to pay higher wages, I just find new employees.
But if my employees started campaigning for, not higher wages, but the abolition of the wages system...well....It seems to me that the SPGB are a vanguard, but only a vanguard of the truth. The problem the SPGB has - and I see this was mentioned earlier in the thread by TomR77 - is that in telling the truth, they are telling people something they do not wish to hear. That partly explains their lack of success in generating a significantly larger membership.
However, I can see Proper Tidy's point, and I think perhaps GD and Robbo and other SPGB'ers need to pay more heed to it. What Proper Tidy is saying is that by campaigning for both achievable improvements and reforms, and for 'transitional demands' which would weaken capitalism, this would demonstrate to workers their potential as a cohesive group and gradually encourage the development of their consciousness as a class and understanding of the socialist case. This makes sense, perhaps more sense than simply believing you can persuade people of an abstract case.
But, the problem with Proper Tidy's position remains this. The strategy he outlines has been tried before. OK, not in the same way, but in a similar enough way to raise legitimate scepticism. By campaigning within capitalism, you risk becoming a radical capitalist movement rather than a socialist movement.
So, who do I side with? I happen to think the two positions are, to a large extent, complementary. I don't think it's necessary to be one or the other. It's a shame there isn't more unity among socialists/the Left. That would worry people like me more than this endless bickering over details.