Yes, the claim is justified by economic theory.
On this site, we have a strong preference for empirically based answers.
An ideal answer to this question would be an actual experiment where they compared two airlines, identical except that one had hidden-city ticketing encouraged, and one where hidden-city ticketing was eliminated, and compare the prices.
Such an experiment is infeasible, and we are forced to fall back on theoretical hypotheticals, conducted by experts. [Economics.SE is a site where they are happier with theoretical answers - which is a strong reason for the suggestions this question would do better there.]
A 2012 paper Hidden-City Ticketing: The Cause and Impact looked at this question using mathematical models.
The models make many simplifying assumptions, but the results support both the existence of hidden-city ticketing opportunities, and that taking advantage of the opportunities will have impacts on the price.
We show that the decrease could be as much as half of the original optimal revenue, but it cannot be more if the airline takes a hub-and-spoke network. Meanwhile, as a result of airline’s reaction, the fares to the final destination of a hidden-city itinerary will rise, which eventually will hurt the passengers.
[...] although the airlines have a strong incentive to prohibit hidden-city ticketing, passengers may ﬁnd it attractive since it instantly saves their money. However, in a long run, using the hidden-city ticketing may also hurt the passengers through the externalities that the behavior causes. For a hub-and-spoke ﬂight network, if hidden-city ticketing is fully admitted in certain period and all passengers take advantage of such opportunities, the optimal fares to the spoke cities will increase in that period. The rises in those fares not only immediately hurt those who travel to the spoke cities, but also signiﬁcantly reduce the profitability of airlines for serving those spoke cities which in turn may result in a reduction or suspension in service towards those cities. Therefore, our result suggests that in the long run, the use of hidden-city ticketing may also decrease travelers’ benefits, creating a lose-lose situation.
Whether you trust such results depends wholly on whether you trust that the simplifying mathematical assumptions used in the model still adequately describe the real world. However, such a result seems to be a reasonable justification to support the claim by George Hobica.