The NHS should not be there to "pick up the pieces" after people fall ill because of their lifestyle choices, said the Welsh health minister.
Mark Drakeford said people needed to understand the consequences of becoming obese or drinking too much.
He backed one Welsh health board's policy of making overweight people attend health courses before being put on treatment waiting lists.
A BBC Wales poll found 82% people thought the policy should be extended.
The survey of 502 people marks the start of a new season of BBC Wales programmes called Live Longer Wales about people's lifestyles.
In one programme, Mr Drakeford denied claims of a "nanny state" claiming that "what the state does when it helps people to understand the consequences of their action is not nannying at all, it is acting as one responsible adult would to another".
In July, Cardiff and Vale University Health Board launched its weight management programme saying improving weight before an operation gives a better outcome.
Under the new policy, anyone who wants elective surgery with a body-mass index (BMI) above 40 must have been "offered, accepted and completed weight management support" before being added to the waiting list.
Tam Fry, spokesman for the National Obesity Forum, an independent group looking at the treatment and management of obesity issues, has criticised the weight management programme and warned the drop-out rate could be high.
He said: "I think it's ridiculous and the reason that it's ridiculous is if someone is morbidly obese there is no way that sending them on a course is going to reduce their size sufficiently.
"Cardiff and Vale stress that the patients need not have lost weight [by the end of the course] so what's the point of sending them on a course?"
He said bariatric surgery, which involves stomach size reduction, was a first option for weight loss.
Mr Fry said the cost of the surgery would be recouped by a saving in the cost of treating diabetes and cardiovascular problems in obese people.
Speaking about the poll results, he said: "That just reflects the stigma which is attached to fat people.
"The immediate reaction for the main part is that if you are fat, it's your fault and you should pay for it yourself and you have got to dig yourself out of your own problem."
But Mr Drakeford said overweight people were less likely to benefit clinically from some operations.
He added: "If you don't put yourself in a position where that treatment will be effective then that treatment won't be available to you."
He said he was "not in favour of penalising people", adding it is "more than education - it is about motivation".
"And it is about persuading people that if they want to live longer and they want to live healthily then that means eating better, moving more and drinking less," he said.
Live Longer Wales: The Shape of Wales is on BBC One Wales on Monday, 7 October at 22:35 BST. It is part of a new season of programmes from BBC Wales throughout October.