An e-mail from a poli-sci grad student:
One reason why young Republicans may appear more moderate is marketing.
My experience is more with the university level than the young professionals level, but it is my impression that activism of that sort is more common in college than the early years in the workforce anyway, and probably carries over into later years anyway. During [college years], there was a constant division among activists on the right between the philosophers — who tended to be ideological purists and favor aggressive or even scorched-earth tactics to spread unvarnished, unapologetic conservative (or libertarian) gospel, and the politicos — who were slightly more flexible in practice and whose goals were more oriented towards improving the image of the Republican party and conservatives in general, incrementally advancing conservative interests, and winning converts when possible. I’ve talked to activists at a number of other schools who report similar divides. These divisions can be extremely contentious and can cause splinter organizations to form.
At liberal universities, in blue states, or both, the politicos can be rather strong, and thus take great pains to portray the Republican party in ways that are more likely to appeal to the available audience. This can be done through actually taking more moderate public views, but also by making less moderate views appear more reasonable even to liberals and centrists than they otherwise would. The image this YDA rep had could simply be a sign of effective marketing by the politicos. This of course means that not only are those who are expressing the more moderate views not necessarily significantly more moderate, but that there likely exists a decentnumber of more extreme conservatives in the activist population as well.
Another possible explanation is a psychological concept called naive realism, the failure to recognize that that their own personal perspectives can bias their perceptions. In the political realm, naive realists conclude that since they are reasonable, well-meaning people and hold certain views, others they view as well-meaning and/ or reasonable should have views similar to them. Thus, a person displaying naive realism will overestimate the degree to which someone who avoids rhetorical excess and whom they like and/or respect agrees with them.
One common activity of the politico types is to engage in bipartisanship — where it works — either through uniting with Democrats on common interests (often mediated by other entities such as student governments or AIPAC) or through friendly competition (debates and panels marketed by and to both sides, contests for charity, public bets, etc.), which are good for public image and/or especially efficient at getting the word out. This means that Democratic activists will be vastly more likely to have personal contact with the more moderate (or moderate-seeming) politicos than the aggressive types. The development of these relationships can bring naive realism into play, and the rivalry between politicos and philosophers can cause politicos to explicitly distinguish themselves from the philosophers by identifying them as “fringers” if they are strong enough to be publicly visible. Again, this not only implies that the impression of moderation is at least partially illusory, but based on a non-representative subset of the activist population.