Answering my own question feels weird, but I have been asked to do so.
There is a lot of cultural context at play. I have been living in China for more than 10 years, and working in a Chinese company where I am the only foreigner. In this company, I have seen only twice an explicit disagreement. In this country, it is very unusual to see children openly disagree with their parents. Obviously it do not mean people always agree or do not have feelings or desires or opinions. But, the Chinese have a long experience in living together and have gained from this experience that openly disagreeing is doing more harm than good. Obviously in some more traditional societies of Eastern Asia, it can and does go way too far, e.g. in Japan.
But, with this in mind, when I go back to my country (France), or watch movie, TV, listen to radio, I am surprised at the amount of open disagreement and arguing I see or hear. It is almost as if agreeing or having no strong opinions on a given topic would be seen as a lack of personality.
And, on the other sides, I see that the people I admire are actually very capable to listen, agree, take the other's opinion in account. This is mostly because they have a strong personality, therefore have no fear of appearing to be weak in the eyes of others, and then do not mind agreeing, or more precisely, allow themselves to express their position only when it is worth it.
Now to the kids. From what I see in cartoons, comics, everything for kids produced in the West, is that we try to build their ego by teaching them to express their desire strongly, asking them for their choice all the time, and so on. Here some people mentioned "family concils". But I maintain that either the choice is unimportant (like which kind of marmelade we buy) or too important to be "discussed" with kids: their opinion on the matter will not change anything anyway. An example of the second case could be "do we move to another country?" What do you want a kid to meaningfully "decide" or "contribute" about such a choice?
So, for unimportant choices I think the best is to not discuss in front of the kids, by fear to influence them in being picky. For important choices, it is unfair to let kids believe they have a voice in the discussion, because they don't, or shouldn't (a kid will not want to move to another country, and will be the fastest to adapt and the happiest once there, essentially kids do not know what's good for them).
I am pushing a bit too far, probably. But I feel it is more fair and saner, and also make kids happier. (Just one more example: we never say we do not like a dish in front of the kids, even when it is disgusting. Result is our kids kind of likeeverything.)