This theory occasionally comes up on Internet forums, the idea behind it being that the Viking attacks on monasteries and churches (as well as the subsequent spread of paganism in England under the Danelaw) had some deeper motivation behind them, namely a kind of attempt by the pagan Vikings at fighting back against Christian conversion attempts. Proponents of this idea would probably take the medieval chroniclers' description of a 'Great Heathen Army' pretty literally.
How much truth is there in this idea?
That has very little, if not no, credence in the academic world. The Vikings attacked monasteries and churches because they were very wealthy (the church was one of the wealthiest establishments in Europe, if not the wealthiest) and were incredibly easy to attack, churchmen were not allowed or trained to fight, Vikings just wanted easy money, they didn't have to attack or besiege. The idea of them being anti-Christian because they were referred to as the Great Heathen Army is looking at it from the wrong angle. The Vikings attacked indiscriminately, but churchmen used the attacks as "proof" God was angry and that people should go to church more. Pretty much all chroniclers back then were churchmen so of course they're going to propel this idea. Evidence for this is seen that many Vikings converted to Christianity when they came to England in the Second Viking Age (970s onwards), why would they set out to destabilise Christianity only to join it?