There is no benefit of the doubt in the laws. Benefit of the doubt to the batsman comes from question the umpire must answer in order to give something out. Generally this will be along the lines of was the batsman struck in line with the stumps, did it pitch on the stumps, was it hitting the stumps etc. If they can't definitively answer yes to that, it is not out and the batsman gets the benefit of the doubt. In this situation, the question is did the batsman obstruct the field? Clearly his actions were intentional because he put his hand in the way of the ball. The question then becomes whether or not the batsman needed to protect himself. I think the answer to that was no and that is the reason Stokes was given out. Clearly this all happened in an instant but that is cricket. Stokes misjudged it. I don't see it as being much different to a batsman padding up to a ball they think has pitched outside leg stump only to find out that it didn't and they are out LBW. It's a misjudgement that costs you your wicket.