i think altcoins will have really good future. but a lot of people think that it will fall in price, but i don't agree with them

We cannot say in general because there are altcoins which are not good or not performing.
I think majority will fail because there is no regulation on the ICO now that is why we are seeing a lot of ICO which some does not really last in the long run.
I believe there is a good amount of fortune and success with the altcoin industry as there is with bitcoin industry. If we put into consideration the quality of ICOs that are recently being listed with their projects and visions, you could clearly see that they aren't just day-trade investments anymore, they are becoming more worthwhile to invest on and suitable for hodlers in the industry.
Until today, I only know some ICO projects really provide for investor profit + the society many applications as the roadmap.
Other projects can provide profits, but almost that amount from the loss of others FOMO bought that coin.
So, for me, it's not a good way for long-time.