Bwana
Player Valuation: £8m
That would lead to situations where there would be no reason to try and block a cross.First situation, if you're onside when your teammate plays it you're onside, no matter what touches a defender takes. Second situation, it depends on the circumstances: Arsenal's goal that was disallowed earlier this season was correctly ruled out because Beto had practically no chance to control the touch. I think it would be really harsh on defenders if every one of their touches was treated in the way you say.
Similar situation happened in ice hockey many years ago when they introduced a delay of game 2 minute minor penalty for shooting the puck directly over the glass. It lead to situations where players trying to score a goal were penalised for trying and they had to change the rule so that it applied only in your defensive end.