Well, that's just something that can be argued about endlessly, because neither side of the argument can really prove anything.
The fans of privatisation will say that profits are pretty small as a proportion of the overall turnover and that in return for these you get the benefits of commercial incentivisation.
The disbenefits of fragmentation are perhaps clearer to see.
As I've probably said a hundred times already in this thread, I was strongly against rail privatisation when it originally happened, and in particular I was against the way in which it was done. All of these consequences of fragmenting the system were pointed out by those arguing against it back then, and most of them have been proven to be true.
There are all sorts of other ways of structuring a privatised or part privatised railway, some of which might be quite sensible - if they deal with those multiple issues of fragmentation.
It's kind of interesting to look at how things worked in the early days of rail, when there were multiple companies, who mostly each owned their track & infrastructure. For example
Railway Clearing House - Wikipedia
It shows that some kind of institution is always needed to co-ordinate the system at a higher level - this is intrinsic to the way railways work. In Europe there are similar institutions, set up to deal with traffic using multiple (originally mainly state owned) systems, such as
Intergovernmental Organisation for International Carriage by Rail - Wikipedia