If it was on just another quiet branch line I'd agree with you without a doubt, but this station has the potential to cause big problems for the performance of the main link between London, Yorkshire and Newcastle with Edinburgh. It would also be somewhat frustrating to spend £20m on a station and however much subsidy it needs annually if only a handful of people ever use it.
Having said all that, if it does what was claimed; that the wider benefits are worth it and the service is reliable to keep links between Edinburgh and England competitive then I'll be the first to applaud it.
a 2011 business case I found claimed 60,000 per annum entries/exits, I believe. (See Part 6.6.33 on:
https://www.transport.gov.scot/publ...s-between-edinburgh-and-newcastle/j196975-07/ about 2/3rds down)