In stations, the commercial activity is part of the overall transport operation. It would be more difficult to separate the two (although not impossible - maybe worth trying!). The question is, why would a rail operator be any good at being a landlord of property unrelated to the railway?
There are numerous examples, in both public and private sector, of organisations catching a cold by operating outside their 'core' business in an attempt to make easy money. There are often problems of expertise - working in an industry the organisation doesn't fully understand - and distraction of management.
As for whether it would be better public or private, as I've said there is little point in getting into that debate here, as (a) the discussion will quickly go way off the topic of railways and (b) it's highly liable to degenerate into a(nother) increasingly strident statement of people's political views. It basically depends on what you believe is the appropriate role of the state, so it can't help being an ideological debate. (And that's even before you get into 'hybrid' models like minority public shareholdings, sovereign wealth funds et al).
"I have strong views, you are opinionated, he is blinded by misguided ideology". Your statement contains the word 'if' which could be debated at length.