There is one thing everyone needs to remember in relation to Thanos and Starlin, and that is that Starlin created Thanos. Prior to the Infinity Gauntlet series, Starlin was really the only writer to use Thanos and he was used sparingly. Once the Infinity Gauntlet was released, Thanos became a mainstream villain in the Marvel Universe. Starlin had or has a particular view of what he wanted his character to be or act like and after Thanos became a mainstream Marvel villain, other writers wanted to use him as the big bad villain in their stories regardless of whether they wrote Thanos' character correctly. There are really only a few writers who understand Thanos' character and who he is, how he acts, and the manner in which he phrases his words. Starlin is the gold standard for writing Starlin's Thanos. Ron Marz, Peter David and Keith Giffen are a step below Starlin but at least they understand who Thanos is and try to stay true to Starlin's Thanos.
If I had a character that I created and spent a couple decades building into what I envisioned my character to be, only to turn around and have others mess my character up, I would try to recon those versions also so I don't blame Starlin at all for trying to return Thanos back into the Thanos he created.
Can you imagine the outrage if horrible writers turned Deadpool into a serious, no talking, Punisher knock off? Or what if Spawn was written as a Dr. Strange type magician by some writer other than MacFarlane? Or it turns out that the Spider-man most of us grew up with was revealed to be clone...errr... nevermind.
The point being is, Starlin created Thanos with a certain characterization of Thanos in mind and to see others deviate from that, I'm sure that upsets him.
So, yes, I believe that Starlin should continue to write Thanos and I wish that others would look at Starlin's Thanos as a model for how they should write Thanos also.