The problem with the privatisation of the railways was the way it was done. It never made sense to separate track, rolling stock and services in such a fragmented way. The way the organisation has developed since it was taken out of the State's hand has done nothing to cure that problem. Additionally, short franchise terms discourage long term investment.
On a general note, with the exception of the special case of defence, the State is usually the last institution you would choose to provide essential services. Almost all State or Local Authority run industries provide inferior service to their privately run counterparts and there is no reason to believe a State run railway system, with constant interfereance from transient politicians, would fare any better.
The two major milestones in the UK's rail industry (the "Big Four" Grouping in 1923 and nationalisation in 1948) both occurred when the system was in bad shape following the world wars. In WW2 in particular the railways took a terrible hammering whilst managing to provide essential lifelines shifting troops, civilians, goods, raw materials and war supplies on an unprecedented scale. It was probably only government that could have taken on the system and renewed it on the scale required as no private investors would have gone near it.
Today the situation is entirely different. Whilst I agree that it is not being run as well as it could be I have used the railways almost all my life, including over thirty years of daily commuting, and I know that the services provided now are far superior to those provided thirty years ago. Measures need to be taken to address the shortcomings of the current system but handing the train set back to politicians to play with is not the answer.