added tag "controversial"

I don't think that either the "lie" or "controversial" tags are appropriate here. This is a statement. It could be Tom saying to Mary: "We must observe the rules." (and then Mary replies "No way Tom, go to hell!") There's nothing controversial about it. It's a simple statement.

everything is a simple statement, then...

Not everything. If I say, "All birds are not mammals.", that's a universal statement.

"we must observe the rules" sounds to me like a universal statement that dictators should love...

If you think that it's controversial, I don't really mind.

Yep...

I don't understand how can this be controversial, much less a lie, when "We" might refer to any group of existing or unexisting subjects.
@sacredceltic: If you're going to tag another person's sentence as "Lie" or "controversial", I would ask you to wait first for that user's agreement, or at least explain the reasons to it, which are not "sounds to me like a universal statement that dictators should love..."

I'm sorry but I'm not going to do this.Rules should not be changed all the time.
The former rule was that advanced contributors may tag.
The new rule is that they must comment that they do so, and I agreed to that.

@sacredceltic: I don't make the rules, nor I am any kind of ruler. What I'm asking is for a little courtesy when tagging a user's contribution as a lie, but it seems I'm asking too much.

That has nothing to do with courtesy but with your conception, totally subjective, of what is a sentence and what is a tag. Sentences are not sacred cows and are a public expression that are never neutral and often illustrate it's author's agenda. They're propaganda and are often lies and controversial, but many people don't realise it because people tend to take things for granted. It's good to open their eyes...
Tags, on the other side, are no desecration and do not belong to sentences owners but to the public. Sentences owners are no better judge of what applies to their sentences.
I sometimes wrote things myself of which I hadn't realised all the implications. Tags made me see it. Sentences escape their authors and that is good.

To me, keeping people blind and mute is not courteous, it is just slavish. Your kind of courtesy is good for lambs. I'm a human being.

These sentences were originally written by students. See http://www.edrdg.org/wiki/index.php/Tanaka_Corpus I doubt they had a big agenda.

Agendas are sometimes subconscious. Some people are more subservient and conformist, others are more rebelious. That's the controversy. The fact that you are unaware that something you write is controversial doesn't make it less so.