Casino house games are set up in a way that the player is guaranteed to be losing in the long run (all of the player's decisions have negative expected value). So maybe trading is more similar to poker because in both of them it's possible to have positive EV but they still have many of the problematic aspects of gambling such as:
- uncertain outcome
- opportunity to lose or win large amounts of money
- some element of skill and the opportunity to "have and edge"
- confounding skill and luck - it's easy to attribute your wins to your skill and your losses to bad luck
- need for emotional regulation to avoid making bad decisions (also known as tilt)
- need for emotional regulation after a session to deal with large losses (or even large wins)
- the fact that you can make good decisions and still lose, in fact this will happen a lot
- the randomness of the outcome and all the associated cognitive biases are prime factors in creating addictive behavior (often to the point where it's problematic)
That's why I would label it as gambling, which doesn't necessarily mean that it's bad. But it's important to be aware of the risks and know that most people's personality and their emotional and mental tooling isn't well suited for it.
You can engage in gambling or speculation when trading forex, because it enables both activities. There are rational reasons to engage in speculation, whereas there aren't any to engage in gambling. Generally the test of rationality lies at the line of information asymmetry: do you have information which the market does not? Then you can engage in speculation and positively inform price discovery, which contributes to the well-functioning of the market. If you do not have superior information and you're not trading on the fundamental value of a thing, you're gambling. There are similar tests to distinguish gambling from hedging and arbitrage, both of which also comprise legitimate economic activity
Graham himself acknowledges in that very book that speculation is a necessary function for markets, because someone needs to accept risk in order to keep the value machine running (i.e. empower short term price discovery). His primary thesis is not that speculation and gambling are equivalent; rather, that as an individual you are more likely to be gambling than speculating.
While modern perspectives on this topic do split hairs, the generally accepted view is that speculation and investing operate along a continuum. Strong opinions to the contrary tend to be rooted in moral and ideological disagreements, not economic nuance. It's not particularly useful to condemn speculation as gambling because a lot of legitimate and useful investing is very risk-tolerant. A much better heuristic is whether or not it's an individual or a firm engaging in the trading.
It's zero sum, you don't have any real influence on the market if you're at the "give it a trial" level, and you don't have any knowledge advantage over other actors in the market. (cf. investing in stock categories you understand, which has the risk of losing money and significantly overestimating your ability associated with gambling, but does at least have a realistic prospect of an overall upward trend in prices and some possibility you can understand certain relevant things better than the big institutional investors moving the market price)
There are practical reasons to trade forex like a multinational company hedging against currency movements causing income to fall in one part of the world, but that doesn't sound like what your brother is doing...
If, as I'm guessing is the case with your brother, you trade with the hope/expectation that a rate will move towards you in the future and you'll profit from that rate move, then that's just common or garden gambling.
But it's also used to buy or sell currency because you cash in that currency, hedge the forex component of an asset/liability, make a market etc. Different people have different use cases.
Everyone I know who has gone into forex trading has lost everything they owned (admittedly this is a smallish sample). They seemed to think they had figured out some smart system, but they all blew up in the end. Very dangerous.
If it was a reasonable realm to make a lot of money in, the ivy graduates at hedge funds and IB’s would be doing it, not Joe Schmo who is paying for an ad for you to take his Forex class.
You are largely having your deals set by your counterparty which is not what you want to have.
It’s gambling for most people, and crosses over to speculation for a limited population of people with domain expertise.