Investment sites is pretty safe, why I said this? Because this is a business model
No it is gambling with someones else his/her stake at risk. when it gos all well you get your cut but also the first to burn when it gos wrong.
What a very accurate explanation you have here, I assume you've been scammed so many times already if you have this kind of mindset. Not all of the investment sites are legit, not all of the businesses are safe to invest, you have to carefully observe their movement if they are legitimately processing their clients money, you have to consider so many things before you could say that a certain investment site is legit
I think what he wanted to mean is that you do not have to be wise to invest into a casino because its just one click and you are done and with house edge you are going to win on a long term time. Whereas some of the other investments requires extensive research if you are lucky and there is no whale winning a huge amount then you will see profits almost daily increasing your money as well.
Some investments (almost all) requires a lot more than this, just putting your money in and waiting until your money is where you want it to be is not enough in many other places whereas it is in casino investments. Trading and investing into coins for example requires a lot of reading the charts and topics and what happens and all that, casinos are not like that, its a system where the house rigs the game and wins almost always.