The phrase "a legitimate topic for" is correct and usable in written English.
You can use it when discussing subjects that are considered valid or appropriate for a particular context or discussion.
Example: "Climate change is a legitimate topic for debate among policymakers and scientists."
Alternatives: "a valid subject for" or "an appropriate issue for".
We are surely sophisticated enough to be mindful of the trick the Fancy Bears, almost certainly connected to the Russian state in some way for all the denials, are trying to pull in bringing together the two separate issues while also acknowledging that the grey area of TUEs is a legitimate topic for debate.
Therefore, discovery was not a legitimate topic for philosophy of science.
The methodology of discovery is a legitimate topic for philosophical analysis (section 8).
Many philosophers maintain that discovery is a legitimate topic for philosophy of science while abandoning the notion that there is a logic of discovery.
(Which is a legitimate topic for civil discourse -- discourse that I hope will come in the next innings of play).
but as much as we might not like to admit it, incest does exist as a subject (in books, movies, as well as in sex columns) and is a legitimate topic for a sex columnist to address.
Methods for defeating totalitarian Islam are a legitimate topic of internal liberal debate.
This is literally the Bible of politics for people whom think the Bible is a legitimate topic of discussion when it comes to politics.
"But he has said it's a legitimate topic of discussion.
"Now, in 2015, after decades of disappearing underground, MDMA is once again a legitimate topic of mainstream science and medicine".
The relative foregrounding of men in anthropological studies became less acceptable, and women's experiences became a legitimate topic of scholarship.
