The common argument would be that, unless you set it up as a co-op/full profit share or never hire employees, you're extracting value (exploiting) from what your employees' labor earned the company.

Missing from both sides of this argument, IMHO, is BATNA.[0]

[0] https://en.wikipedia.org/wiki/Best_alternative_to_a_negotiat...

Building the SaaS is work, responding to customer support tickets is work; collecting rents every month on a capital asset you own is not work.