A huge amount can be done to improve access to, and the regularity of, screening.
I could not tell you what fraction can be attributed to the fact that it is criminalized, but that it one of the things that must be done. Clearly, that will make access to screening easier. Screening has to be made available in places where people need it. We also have to encourage regular screening.
People do not go to be screened for all kinds of reasons. But the reasons are more to do with the organization of the services. There is also the stigmatization factor, and the fear of knowing one's status. Any obstacle that can be removed will help us move closer to better knowledge of HIV status.
Unfortunately, no study comes to mind that would let me tell you how many people could find out their status if at least that legal barrier were lifted. Of course, it would be a step in the right direction for us in achieving our public health objectives; no doubt about that.