Good question. To address some of your concerns:
but I still see lot of courses about technical analysis, and even people using it.
Sadly, this is meaningless; simply because courses, journals, and practitioners exist for any given field doesn't validate that field.
They have the advantage of being easy to learn and they claim themselves as following the "behavioral economics" theory.
Behavioral economics is distinct from technical analysis. The former is based on empirical data stemming from psychological study; the latter, off strict historical price data, and nothing else. In fact, the "founder" of technical analysis specifically said he wouldn't let any outside factors- anyone's mood, the weather, a catastrophe, etc.- get in the way of his analysis.
Is the traditional & simple TA somehow valid? I'm asking about the one that uses moving averages, graphs, momentum lines to try to predict market moves.
The answer to this question carries a survivorship and success bias; you're much more likely to hear from traders whose luck turned out well with technical analysis, rather than traders who haven't done too well. For success bias: suppose you had 10 traders who did well/poorly with technical analysis strategies. That doesn't really prove anything. Some really long and detailed studies have shown that tech analyst traders haven't really outperformed anyone.
The behavioral economics theory is valid and 2 people won Nobel prizes because of that, so I'm not arguing its validity,
Unfortunately, winning the Alfred Nobel Prize in Economics doesn't validate a theory either.
...but its consequences or usefulness as an investment method.
A good question. I highly encourage you to ask this on other StackExchange sites in addition to this one.
Please take into account not only a highly efficient market (eg, the US), but other smaller and less efficient markets (I'm from Argentina).
Here's the thing: fundamentally, I think the intellectual grounds supporting technical analysis is, at best, very weak: you can't drive forward by looking at your rearview mirror, and that's effectively what technical analysis is. Empirical study has shown that trying to predict the price movement of a stock isn't that beneficial with tech analysis; however, many traders use the techniques anyway. I believe that if one was to use tech analysis to gauge the positions of other traders who use tech analysis, that trader/investor could hedge accordingly. In other words, if you and I are traders at different firms, and I know you use tech analysis, I will use tech analysis to guess what your position is on some security. When I call you up to make a deal, I'll have a good idea what your valuation is of the security, and I could negotiate a price accordingly (or not bother at all), while you may not necessarily know my position. Think "game theory."