Patients should wait no more than 12 weeks to start treatment agreed with hospital doctors under a law that took effect in 2012.
However, MSPs heard yesterday that health boards are not managing to meet this pledge for all patients.
Nor could John Connaghan, NHS Scotland performance director, tell members of Holyrood's Public Audit Committee when the pledge will be met.
Hugh Henry, committee convener, questioned the wisdom of parliament and the "stupidity" of politicians for creating a legal right that cannot reasonably be enforced.
In an intense exchange with Mr Connaghan and the new chief executive of NHS Scotland, Paul Gray, Mr Henry said: "A legal guarantee is far more than a target, it's something that is enshrined in law.
"Now that legal right is not being met, so you are not fulfilling the will of Parliament, the boards are not implementing the will of Parliament and patients across Scotland are not having their legal entitlement observed, guaranteed or implemented.
"Is it not a farce that you have a legal right and you can ignore that?"
Mr Gray stressed the legislation was not being ignored, but continued: "I accept the points you make, and we are working to get ourselves into a better position.
"The Parliament also made its position clear on how they thought that legal guarantee ought to be implemented and the redress that was available, and we work within that."
A delayed patient can "ultimately seek judicial review" or complain to their councillor, MSP or NHS board, he added.
Mr Henry said: "So the rich, the articulate and the confident will be able to pursue some redress and the rest of the country can just go whistle?"
Mr Gray said: " I take your point but I can only work with the legislation as presented in Parliament. I do not hold the view that the poor can go whistle."
Mr Connaghan said he was "cautious" about giving a guarantee that the legal obligation could be met at present, but may be more willing in future.
Mr Henry said: "I'm questioning the wisdom of Parliament in introducing legislation that has been ignored, that has not been met, because it begins to question the sanity of politicians when they bring in laws that can be blithely ignored.
"I understand your frustration, because you're saying you cannot give 100% guarantee that the law will be implemented.
"Now, in a sense that poses a question about the stupidity of politicians making laws that cannot be implemented."
The Patients Right (Scotland) Bill 2012 was introduced by Deputy First Minister Nicola Sturgeon and passed with full cross-party assent by the Scottish Parliament in February 2011.