However, even in Europe, the direction of socialism for step-by-step reforms through the parliamentary route, e.g. Social Democrats, historically favoured policies building up a wide middle-class. Myself, I think the self-defeating nature of this project could have been seen on the onset: the have-some will have a tendency to defend what they have, and hope they will rise further, thus a significant part will end up supporting the have-mores against the have-nones. [...]Thus to a large extent I view the current doldrums of the European centre-left and the plague of Third Wayism as a logical consequence of core Social Democrat strategy from at least 60, but perhaps 120 years ago.

First, I think you're wrong on the dynamics of building up a wide middle class. It is precisely at the time that the have-somes felt most secure and upwardly mobile that they were most willing to support anti-poverty programs (i.e. the sixties through the mid seventies). The backlash came once they started feeling their prosperity threatened.  You also can't really expect for a large majority of society to vote to lower their own living standards substantially in favour of a minority.

In times of extreme economic crisis, i.e. the Great Depression, the declasse have-somes in Europe reacted by turning to the extremes - the anti-democratic and radical parties of the left, but especially the right. In America they turned towards the moderate left in the form of FDR. Neither is a particularly hopeful example for the radical left. On the other hand the example of the postwar boom does suggest that the incremental approach which starts off by reassuring and helping the broad middle can pay large dividends for the poor as well.

Which brings me to my final point - the historical attitude of the radical left towards fundamental democratic values has tended to range from ambivalent to very hostile which in turn hurts their popular appeal.  That stems  in large part from a conscious or unconscious understanding that the radical alternative is very difficult to achieve without the use of the gun and the torture chamber on behalf of a self appointed and unaccountable elite against the population.