You have asked this question with regard to criminal justice, so I will answer it in that context. However, the answer is really the same in every context. Lack of resistance is not consent. Consent is voluntarily given; lack of resistance is not necessarily voluntary.
Let us think for a moment about a situation in which Person A gives money to Person B. Here, we can see the difference between consent and lack of resistance. If A and B are friends, B might come to A and ask for a loan. A might agree and they will go down to the ATM to get the money. That is consent and it is voluntary. Now imagine that A is at the ATM when B comes and threatens him with a gun. A does not want to die or be badly harmed so he does not resist. He knows he cannot resist a gun effectively and he would rather give up the money than be harmed. He gives B the money. But this is not really voluntary. Without the coercion represented by the gun, he would never have given B the money.
Therefore, lack of resistance is not consent.