The reason some people called trading as gambling is because of the risks it has. Trading is very risky to the extent that almost all traders are losing. It is better for some people to avoid trading and be patient and invest in bitcoin when the price has already fallen significantly than to trade and continue to lose. Although, some people are good traders but they are not many.
You're right on the reason why people compare trading to gambling, both activities has similar thing in comon, the risk invyolve in both activities is very high, as a matter of fact there's no assurance that your profit is assured, profit are in both stuffs by chance or will I say luck, yea there's a high possibility of losing in trading and gambling, I think there's no difference between the two, personally I think there's no need of individuals being too quick to make quick money in Bitcoin as such seeing trading as the means to achieve that.
Although people are entitled to their decision on whether to invest in Bitcoin for a long-term or to get involved in trading which we see as a short term investment, your suggestion is very good if buying when the price is down is what will prevent people from trading fine although am an advocate of buying all the time with DCA method without minding the price at any given time or period, I don't know much about trading and I don't think I to even get involved but what I know is that every trader has either lost or will definitely lose so I don't think there's anything like good trader though I stand to be corrected.