Why one shouldn't trust all altcoins is that most of these altcoins are being fronted by scammers. They float these projects, lure investors and they pack up afterwards. One just has to be very careful.
One can just avoid dabbing in altcoins completely. That way one can avoid getting scammed by these methods. Or they could learn properly how these scams operate and then use that knowledge to inform others.
Generally speaking they take advantage of the anonymous nature of crypto and they don't have the morals that legitimate humans have. So do your research but you can assume that the project will fail and you will lose your money. I still consider a loss to be a loss and not that it was money I could spare - Nope, money is never spared. I would rather invest in other asset classes.