Questioning motives is always reasonable, but concluding that their motives are evil is not justified here (i.e. the answer to the question cannot reasonably be a conclusive "it's evil"), because the claim that you are then making is ridiculous.

Serious economists who stand to gain little-to-nothing from espousing right-wing economic policy have pushed for privatisation for decades - opposed, of course, by many serious economists who espouse left-wing economic policy.

The "evil motivations" conclusion either has to accuse all those economists of being evil (for what gain, we do not know) or it has to claim that a person's motivations for putting forward right-wing economic views is entirely inexplicably ceases to be "honest but misguided" and becomes "dishonest and self-serving" in perfect correlation with what they stand to gain. That's not reasonable: if it's possible for someone to honestly hold an opinion, the mere presence of them having something to gain from that opinion doesn't turn it dishonest.

This is before we get to actually assessing whether politicians actually stood to gain much from privatisation. John Major, for example, who oversaw rail privatisation, was born to a middle class family that later fell on hard times. He wasn't born with a silver spoon in his mouth and attending parties with bankers. That brief analysis can't tell you everything about his motivations, but it should make it more realistic that his sympathies lie more with ordinary people than with the ultra-rich, even though he oversaw policies which we know, or at least believe and can argue for, hurt ordinary people.

So it sounds like we agree? Privatizing advantages the bigger, wealthier, investors.

What I disagreed with is that the belief was mad. You've just explained a lot of ways that the belief was wrong not that it was mad. We agree that it was wrong, so this didn't do anything to convince me that it was mad, and I still don't agree with that.

If I've understood this line of argument, you're raising objections to privatisation, and then concluding "since privatisation is a bad idea, anyone who believes it's a good idea must be mad." Do correct me if this is not your logic.

If it is then it's unsound in a way that I see repeated again and again on Lemmy: people who disagree with you on one thing tend to also disagree with you on other things. Specifically, someone who thinks privatisation is a good idea, does not (or did not) agree that any of the arguments you raised were sufficiently strong. It would be mad to continue to think that privatisation is a good idea if you agree with the arguments you made against it.

But merely disagreeing with your arguments is not mad. Just wrong.