Should I have doubts if the organizers of a workshop ask me to sign a behavior agreement upfront?

Plain and clear: Turn around and run.

We know, of course, nothing about your actual event, but that kind of language and mindset is absolutely impossible. Unless you are trying to get into such prestigious circles, of course (what do I know, it might be an Oxford or MIT event for the "best of the best of the best" students in the world...), but you would likely have mentioned that.

This sounds more like a brainwashing event than an earnest academic workshop. As you rightly took good note of the terms in their first mail, you will very likely have either nagging doubts/fears during the event, or, will find that the athmosphere is one of much tension (which is hardly good for learning).

Even though you are "only" a student, you are still an adult human, and a teaching organisation has no business talking like this. They are a service provider and you are the customer. They are nothing without you. You are not a serf labouring to meet a person higher up in the food chain, it should be the other way round.

Even if there were some way to justify the legally binding agreement for attendance and behaviour, a professional would answer your question in a neutral/friendly way, explaining why they need the agreement. They are asking you to sign something (onesided, as well), with a clear threat attached. They do not see fit to explain why and how it exactly it works. This is clear fear-based intimidation, or at least, by their communication, it looks that way.

So either they have bad intentions, or they are just not good at communicating. In both cases, this is in conflict with them trying to teach you something!

Should you be worried about "legal actions"?

Maybe. I deem unlikely that any jurisdiction has specific laws for you not attending a workshop (of course I am not a lawyer and you never know, maybe North Korea's..). Any legal consequence must come from the agreement they make you sign, and you are at the very least entitled to see it before reaching the venue and be put in a position where you are pressured into signing it.

In my humble opinion, I don't think there is any actual legal consequence awaiting you and this is most likely an empty threat.

Should you be worried about "academic actions"

The only thing I can think of is being somehow shun by that specific workshop community and maybe be blacklisted for future workshop from the same organizer. Is this a relevant thing to you? Maybe, if you are "caught" missing any of the talks, you might receive a reprimand.

Other considerations

Without further information I cannot say whether this is a good workshop or a bad one, but there are some obvious red flags.

The language they use in their reply to you sounds unprofessional to say the least. I personally find it quite offensive.

Furthermore, everything they write sounds extremely pretentious. Sentences like:

This course, unlike others is a prestigious and highly demanding one.

and

This is the reason, why *** is spending this huge amount.

and

There are many deserving candidates out there who are willing to leave everything behind and simply be attentive to listen and grasp knowledge from world leaders.

make it sounds like they are desperately trying to convey the high quality of their workshop to you.

This is somewhat inconsistent with what they are trying to project, though. If their course had really such good speakers, whose lessons are so invaluable, why do they have to put an unheard-of clause about attendance, threatening attendees with potential "academic and legal action"?

Why, instead of politely replying to your legitimate query, do they write such a passive-aggressive letter, suggesting that you pass on this because maybe you are not the candidate they are looking for? Do you see that this, too, is a device to have you attend?

If I had to guess, I would think that in the past people got so sick with wasting their time there with pompous self-proclaimed world leader that many left the venue. I am not saying that this has happened, I am most likely wrong, this is indeed a great workshop with a stricter than usual rule and the occasional rude guy answering email, but I would take time to reconsider whether this workshop is indeed worth attending for two weeks. Maybe your time and money are indeed better spent elsewhere.

Were you wrong in asking ?

I think you had a right to ask, but perhaps your email was a little misguided. Rather than providing possible motivations you could have simply asked explanations on what the clause meant and to see the agreement.

If you want to go forward I'd ignore their considerations, as there is little point in arguing with jerks, and just stick with a polite email along the lines of

Dear Sir, I am planning to attend the workshop fully, but I'd like to understand the legal consequences of any agreement I enter into. I kindly request that you send me a copy of the agreement I will be required to sign beforehand and extend the deadline to allow me to read it before giving you a definitive answer.

SCAM!

They avoid answering a valid legal question, try to make you feel bad for asking, and apply pressure to make you ignore the legal issue. If you run a con, that's how you do it.

Bonus points for the random 24 hour time limit.