To say God should make us incapable of lust is to say that he should make us incapable of sin in other regards.
The reason why we have the ability to sin is so that we can love God through our own merit. So that people can be good because they choose not to be evil and actively work against it, not because they have no other option.
The reason why we have the ability to sin is so that we can love God through our own merit. So that people can be good because they choose not to be evil and actively work against it, not because they have no other option.