I was driving into Doha on Thursday doing 100k, the speed limit on that stretch of 3 lane road, absolutely no traffic on the road. I pulled into the middle lane to let traffic merge from slip roads on the right, AND still had cars roaring past undertaking when they had an open lane to overtake!!!!!
I agree you should drive to the speed in your particular lane and slow drivers in the wrong lane are a hazard. However undertaking is extremely dangerous. Thankfully it's punished by a large fine, a friend of mine was fined 6000QR for it (but it was negotiated down to 1000QR, go figure?)

I always get great delight in seeing some idiot weaving across all 3 lanes at high speed only for me to beat them to lights by driving in the correct lane (and reading the traffic ahead of me) for the turning I want. :)

I don't go to mythical places with strange men.
-- Douglas Adams, The Long Dark Tea-Time of the Soul.