Why are social democrats constantly asked to defend Maduro?

It has occured to me, that in almost any political debate where a social democrat takes part (by today's standards, a "radical leftist", by 1980s standards a common liberal), Venezuela and its nominal "socialism" are brought up, so as to demonstrate, in a quite McCarthyite way, that socialism is an evil word. This has been the case with Jeremy Corbyn in the UK or Jean-Luc Mèlenchon in France. They are asked to defend a repressive, authoritarian regime as if it were the sole true propagator of socialism, or else they are seen as "out of touch with reality".