I agree. It is incredible to me that anyone would argue that Amanda's DNA on a particuliar location on the knife suggests that the knife was used in a particuliar way - specifically as a murder weapon. If that is an example of the reasoning that is required to believe Amanda is a murderess color me unconvinced.
Regarding the DNA, we have two samples that are a serious concern, and additional samples that support the allegation that Knox/Sollecito participated in the murder.
DNA on the blade of the knife was analyzed and is consistent with Meredith's DNA. The defense arguments have been that because it is low copy number DNA, the sample should be omitted and, if it is a legitimate match, the sample was on the knife due to contamination. LCN DNA is how the sample size was described using older testing methods in 2007. Today, it is possible to analyze much smaller samples with accurate results. That, in itself, should negate any concerns regarding sample size.
DNA on the clasp is consistent with Sollecito's DNA. The defense argument has been that the DNA on the clasp is a result of contamination, or it should be omitted because there is evidence of more than one person on the clasp.
Knox's DNA was found in Meredith's blood and the defense argument is that Knox stepped in bleach or fruit pulp, not Meredith's blood, and left footprints at Meredith's door, in the hallway and on a piece of glass in Filomina's bedroom.
Knox's blood was mixed with Meredth's blood and was found in the sink. The defense argument is that her ear bled from piercings and landed right on top of Meredith's blood.
In each case, where there is evidence of Knox/Sollecito participation in the murder, we have a different type of excuse. At the same time, evidence of Guede's DNA is accepted as clear proof that Guede was involved - no conspiracy or contamination discussion. Bloody footprints in the hallway from Guede are accepted as footprints in blood - no bleach or fruit pulp discussion.
Essentially, investigative techniques used to gather evidence that implicates Guede were completed according to protocols and there were no errors, but the same techniques used to gather evidence that implicates Sollecito/Knox, per the defense, failed repeatedly.
Now we have additional evidence that Knox handled the alleged murder weapon. The defense will argue that, even though Knox claimed that Sollecito cooked for her and Sollecito claimed that he cut Meredith's hand while they were cooking at his apartment, Knox in fact cooked for Sollecito and she handled the knife as a "chef", which resulted in her DNA at an unusual location on the top of the knife blade.
In the words of Shakespeare: "The lady doth protest too much, methinks."