Well it is true that by giving the absolute power to the majority, you hence take the risk of the majority being wrong.
But a few things allow me to have faith in such a situation:
-First majority doesn't mean 51%. Majority can be higher. It would seem rather logical to write in the first constitution of such a democracy that any law needs 65% of the people vote to get approved. Being hence sure that the people really wants that and not that it's close to civil war with a big 50/50. We can also ensure some stability by saying that changing the consitution needs 80% of approval, hence only crucial changes can be written in the constitution.
-Second, I strongly believe in transformation under responsability. Indirect democracy made people weak and stupid. They're not interested in politics and easily manipulated, because they all know they can't change anything. But if tomorrow they know they have the faith of the country in their hand, I do believe they'll get much more involved on politics. Exactly as the Greeks citizens did thousands of years ago.
-Third, moral is subjective. If more than 70% of the population wants something, who are you to say it's bad? What kind of moral absolute value could you take?
-Fourth, developped countries have a high education hence strong history knowledge and shouldn't tend to repeat mistakes.
Of course I can't guarantee anything, but it's still what I believe.
Addressing the bold points, the fact that morality is subjective is exactly why you need to restrict government to the most basic rights. In the southern US in the middle 19th century, there was widespread consensus that slavery was a justifiable economic model and that black people were inferior and therefore could have no rights as human beings. The notion was so widely accepted that the Supreme Court itself ruled that blacks had no rights under the Constitution. This is clearly an immoral and unjust viewpoint, despite being widely supported. Democracy clearly failed in this instance. The popularity of an idea has no relation to its morality, so simply saying that something that enjoys 70+ percent approval does not make it a legitimate point. Because morality is subjective, we need to limit government to a role of protecting the most fundamental freedoms that everyone agrees every person possesses: life and liberty especially, and most people will also include property. As a nation, we can decide that certain people do not have the right to be free and must serve as slaves for the benefit of the rest of society, and this idea could have the approval of 99% of the population. It is still an evil notion, and the role of government is to enforce everyone's rights equally, and especially to protect the minority who the majority would otherwise take advantage of if given the opportunity. When you have unequal rights, you have arbitrary law, and arbitrary law is unequivocally evil. Arbitrary law is what the American Revolution was fought over, and the Declaration of Independence was an indictment of the British practice of instituting arbitrary law to suit their whims. And the history of socialized government is one that has repeatedly instituted some measure of arbitrary law, because there is no way you can protect all rights equally while also redistributing wealth, because it necessitates infringing some group's rights arbitrarily under the direction of popular government.
You're missing an important point:
You don't have a choice.
You're telling me "it's not because 70% of population agrees on it that it's good".
Fair enough. But then?
If it's not the people who decides, who will? An elite? Lol, we all know what "elite" do...