I believe all rape cases should have undeniable proof that the rape actually happened. Without DNA evidence or when the DNA evidence is contaminated, the case should be thrown out of court. Cases without this evidence are simply a matter of he said, she said and that is not fair to the accused.
DNA is not an absolute guideline of conviction. DNA can give supporting evidence but is in no means a reliable sole piece of evidence for conviction. Analysis can confirm the presence of DNA but not how it came to be there nor how long it has been there. Additionally if the defendant claims it was consensual sex then the presence of DNA has no implication whether this was rape or not.
I do not think that contaminated DNA evidence should throw a rape case out of court. I think that it shouldn't be the reason why a case cannot be tried in court. There are a lot more ways to convict a suspect when it comes to such cases. I think that it would be an injustice to the people and judicial system.
No, contaminated DNA evidence should not, automatically, throw a rape case out of court, because there might be enough grounds to convict the person otherwise. There could be an eyewitness; the defendant could have made good admissions. Contamination alone is not enough of a reason to let a rapist go free.
If evidence is faulty, in this case, contaminated DNA, it does not follow that the person on trial is innocent. The degree to which the evidence is contaminated should be considered before throwing it out as evidence. However, the guilt or innocence of the person on trial might still be established by other evidence. Lack of evidence neither implies guilt or innocence.