Without altcoin, I will not have much bitcoin. I mine altcoin and sell them for bitcoin. I do not mine bitcoin.

I am in the similar situation. I mine altcoins as it is not profitable for me to mine bitcoin directly.

Well but it's risky, right? Altcoin might cost nothing when you want to sell it. But on the other hand it might cost much more in Bitcoin than it was when you mined it. So mining altcoins is almost like gambling IMO.

Bitcoin is self-sustainable and a good stable system.
Bitcoin will still doing good without it. Altcoins are exist is because Bitcoin existance.

Yeah bitcoin never suffer without altcoin, but altcoin is assumed to be the sub of bitcoin so it suffers a lot. I think the price of altcoin has no impact on bitcoin.

Most of the people invest into bitcoin as it has the highest price and the highest survived compared to altcoins. I think altcoins is needed to make large number of bitcoin. As users are trading alts and investing profit into bitcoin.

And also most people who have altcoins always sell their altcoins into bitcoins. so this both coins really connected and altcoin always need bitcoin.

I think it provides newcomers into the Digital currency scene with a bit of excitement and also, developers and punters alike can express themselves through other digital currencies. Bitcoin opened the way to new creativity and modes of thinking and as a monopoly, it wouldn't perhaps grow as it has done. Having these other currencies come into play actually galvanizes more promotion of Bitcoin to the Public as well. I believe it has a positive role to play and also developers can show off their skills to progress in blockchain and other related technologies. 

Without altcoin, I will own very little bitcoin. I buy bitcoin buy selling altcoin. I get the altcoin by mining them.