You only draw for this effect once, even if the number of cards in your hand remains below 2 due to an effect like Deck Devastation Virus.
The effect of "Fabled Ragin" lets you draw cards from your Deck until you have two cards in your hand. You do not draw exactly two cards from the Deck.
If your hand size decreases below two after the effect of "Fabled Ragin" resolves, then you cannot draw again.
Example: While the effect of "Crush Card Virus" is active, if you draw cards by the effect of "Fabled Ragin" and you draw a monster(s) with 1500+ ATK, then the monster(s) is destroyed and you cannot draw again.