I'm most definitely a DSA supporter but fa2fi identifies a key feature of some of Onyx's posts!
The only way ANY station serving the airport could be justified right now is if it was part of an integrated transport plan serving not just the airport but the local Finningley community in the same way as those at Adwick and Bentley do. But there isn't the residential demand for it that I know of it. And even if there was I doubt placing it near the airport would make it handy for those residents! Anything benefitting the airport must benefit the local Doncaster community first and foremost. The FARRS does that and so does the Business Park near the M18. An airport station wouldn't.