That's yet another of the problems for them . They realise that it has been done elsewhere ,earlier and with bigger rocks ,and where glaciation can't be used as a possible explanation .
Similar feats have been done in the recent past with much heavier stuff with the same type of equipment as would likely have been used in prehistory .There are ethnographic accounts , pics and film . It doesn't prove that the bluestones were transported by punters but it certainly shows it's not a problem . When the discussion turns away from glaciology it gets embarrassing. A bit like archaeos or footballers discussing the economy .