As long as it is within the rules, it's fair IMO. Obviously they know the penalty for a deliberate handball, but it's a price you are willing to pay to potentially save a goal.

Similar things happen in other sports too. In American football, defenders will deliberately interfere to prevent a receiver from catching a touchdown pass. In basketball, players will intentionally foul a bad free-throw shooter. In baseball, pitchers will intentionally walk the best hitters. It's all within the rules.