The usual dichotomy is that if you control the platform, you can't sell using it will lead to an abuse of market power.
Eg "If we're massively successful in building/buying the water distribution network in $city why hamstring us?" Is an argument that holds no water.
There's a decreasing long-run average total cost curve for systems software. Which is why microsoft dominated the desktop for so long and why there are only 2 viable phone operating systems - where the veondors and controllers of those operating systems use their massive market power to compete in how much abuse of the users they can dole out.
I realise trying to explain conflict of interest and market power abuse to fans of a company that literally tax the revenue of anyone selling software on their phones and tablets, then destroy success by competing with it unfairly abusing that platform control, is doomed. But it remains a very strong economic argument based on the technical defintion of market failure accross the spectrum of economics as I studied it late last century, from Friedman to Keynes.
As ever, anything that contains "...with a computer" prevents most adults from engaging the critical thought region of their brain. [1]
[1] I'm really happy to have people disagree with me on specifics if they can explain why this thing "..with a computer" is different and needs to be treated differently in law and policy to the same thing, contstructed with thousands of people, filing cabinets, paper and old-school dial-up telephones. Imagine how you would provide the service with the latter. What policy is appropriate? What law is appropriate? When should that law be enforced? Then apply just that to the same system with a bunch of servers and software.
If that "same system - computerless" analysis and case was made each time, we'd have much more sensible policy and policy discussion. I can dream, right?
I wrote this with a computer. :s