Profit earned is all that counts in the end. Note that I'm not saying that day trading is profitable for everyone or it is a losing game for every trader out there. But it simply can't be gambling if you accept that trading as such is not gambling. There is no other choice because all price growth starts small, even profits from long-term investment are made of small price moves. Capitalizing on the volatility which results from these small moves allows you to earn higher profits because there is no growth without corrections, however small those can be. Add to this that you can't always be right in your assessment of the future growth and even more so in respect to the extent of it.
First of all you talk about capitalizing on short term volatility like it is easy to do, and like people are capable of doing it consistently. When you buy an asset with the intent of trading it intra-day, how do you know it is going to go up and not down? You can lose money as easily as you gain it. There is no way to accurately predict price movements on this small of a scale CONSISTENTLY. Day traders will lose just as often as they win over a long enough period of time, and because of fees, this will end up putting them on the losing side overall.
Also, profit earned is NOT all that counts. If I am day trading in the stock market and earning 8% ROI in a year, but the S&P500 returns 12%, all of my work figuring out what to sell and buy and when, was just a waste because I could make more profit by just holding an index fund. Same with bitcoin - if you day traded bitcoin in 2017 and made a 200% return, you have failed because you would have made more money by just holding bitcoin. All of that day trading not only failed to help you make money, but it resulted in a massive amount of wasted time and wasted potential profit.
As I have written in OP, there is a lot of confusion about day trading. Day trading doesn't necessarily mean that you buy and sell all you have within just one day. Day trading refers to your trading activity, how many trades you make daily. In this way, there is no precise definition of it. It is a loosely defined concept where many different trading strategies fit. You determine the trend in the same way as you do for long-term holding, and then you capitalize on short-term volatility. As long as you can make profits consistently as in arbitrage, which is also day trading, it is not gambling. This is the difference I want to point out.
I never said, or implied, that day trading meant buying and selling all you have. However, it DOES involve buying and selling within one day, BY DEFINITION. That is what day trading is. Intra-day trading to take advantage of fluctuations in price within one day. This is not a misconception or anything, this is literally the dictionary definition of day trading:
https://www.merriam-webster.com/dictionary/day%20traderYou are not reading what I wrote. It does not matter if you profit, that is meaningless. The only thing that matters is how you perform compared to the market. If you profit but you underperform the market as a whole, your strategy is failing.
Day traders do not determine trends the same way as long term investors. Long term investors look at fundamentals and day traders do not because fundamentals do not affect intra-day price movements.
Day trading is gambling, period. It is 100% luck based. Anything that is luck based is gambling. Long term investing is NOT luck based, and therefore is not gambling. It's that simple.