Psalms is part of the OT law that Christ took out of the way, Col 2:14 making that whole law inactive, of no effect. The OT law cannot justify use of IM no more than it can justify polygamy or slavery. If you hold David up as justification for IM then whose to stop those that hold David up for having multiple wives and concubines. Those slave owners back during and before the Civil used the OT to justify slavery.
I will also add to say that the Psalms promoted the bolded above is blasphemous, contrary to the truth of the inspired songs sung in way of worship and you will pay for making such a comparison!