Yes you are correct, Bitcoin can exist continually even without altcoin. But one thing for sure the no.1 will affect are the different exchange platform, they will get less profit into it.

Bitcoin is the mother in crypto currency and without alt coin i think the price of bitcoin would not too high like the price right now because there is no other coin trying to get number 1 in crypto currency.

I don't think that without altcoins Bitcoin would have no value, but I think they are helping Bitcoin to be more adopted. People, young kids especially, like to collect some altcoins because for some reasons it looks like you have more if you have say 1000 DOGE instead of 0.00037 BTC.  

After spending some time earning altcoins they realize that collecting Bitcoins is better and hence Btcoin gets more adopters.

Altcoins definitely added some popularity to bitcoin's fame. I am glad they exist.

Because I have seen lots of threads that are about ICO scam then this makes me a bit afraid to invest in any ico of altcoins.
But when I check how much the community has invested in these ico it's unbelievable and sometimes it reaches millions of dollars.

did you know that most of altcoin using bitcoin as a base currency and encourage people to invest into the specific altcoin or i say investing in an ICO using bitcoin? so it's definitely a free-advertising for bitcoin and could make bitcoin even more popular,when an altcoin just make an advertisiment out there to make people investing so bitcoin will be automatically represented

I don't believe that altcoins help bitcoin to grow but actually altcoins are used because they are connected to bitcoin and the users of bitcoin trade altcoins so that they can earn more bitcoins, so the prices of altcoins depend on bitcoin but not the price of bitcoin depends on altcoins.

i think bitcoin can survive and still used although without altcoins
but without altcoins crypto trading world will not created
so we cant get profits from altcoins

I do not really know what than would happen with the bitcoin, I think the price would be a lot lower plus that it also would not be so popular as now.
Trading would also not be like it is now.

ethereum was really promising since it has a huge support from the market the only problem is that when can they still support that coin. XMR is dominating in the market right now and it surpasses ETH at the moment.