Both in Stocks and Crypto trading, nothing is wrong with day trading, some traders are making huge amounts of money through it. It also depends on what you mean by day trading because there are many strategies of day trading, we have scalping, holding the position for minutes, while others might hold their position for hours and even for the rest of the day (about 23 hours). The higher the duration of trading for the day trading, the better and less risky it is. And once your strategy is good enough, you will be winning regularly.
I don't think that anyone thinks that there is something wrong with day trading, it's more about how difficult is to day trade and be profitable. Many people are trying many strategies, but the fact is because of bad timing/greediness/wrong information/etc many people are losing money, simply profit they make can't cover losses. What many people don't realize is if you wish to make a profit with trading you need to worm up your chair, you need to invest time and be active in following your chosen pairs. I guess it can be like a full-time job because the more active you are the higher your chances are of having successful trades. It's not a "get quick fast" scheme, people think they can trade at any time by picking random pairs and it's all! Well, things don't work like that in trading.