No . Using bitcoin for current billing is often not widely used. Many investors buy bitcoin for their investment purpose instead of using it for payment methods. The daily payment method is mainly traditional currency.  So , rising bitcoin demand will not diminish the value of the domestic currency.

How could that happen if we are always converting every crypto currency into USD? 
It is the truth and specially with bitcoin which is like a commodity only and not a currency for a lot of people here.

It just became a trading tool to get more USD which is getting me worried. It may stay like this for a long time. It will not weaken the fiat system but more stronger.

Sure the native currency will fall down if the usage of Bitcoin increase among cryptocurrency community or among the masses. Yes, people feel that the transaction that's been done through fiat is not secure so, they crave to that transaction done without a trace. Yes, some cabal never want to see Bitcoin live as it post a threat to their economy and given freedom to the people by the people.

Bitcoin and Fiat currencies have no connection when it comes to their price/value/volume..
And none of the two can either affect the others price nor value..

Fiat currencies are regulated by the government and reflect the economy of a nation,it wields so much power in their native country and the bitcoin just can't reduce it's patronage..

Bitcoin isn't regulated by the government and reflects individuality,as individuals on the system determine it's price/value..

The bitcoin is growing faster than expected with far more adoptions everyday,but it is in no competition with conventional currencies

I think it will not happen in short terms, but it can happen in long terms...

yes, the value of the native currency will fall when the demand for bitcoin increases higher, the function of fiat will be limited, and will only be used by some primitive people, and some people don't like the growth of bitcoin and they try to make FUDs that can make bitcoin fall.

I think, it's not important to answer their opinions, it will only waste time, and they will regret when bitcoin dominates every transaction value.

I'm no economic expert, but won't supply and demand impact value? If we all start using bitcoin, and there will be less demand for fiat, won't its value be affected?

For me, I don't really think that the usage of Bitcoin will come to reduce the value of the native currencies. Because, fiat currencies are controlled by banks which is under government. The government too, will not let this happens because they will take an immediate action towards this. And for my instinct, this will only have a possibility, if and only if the crypto currencies will truly and definitely replace the use of fiat currencies.

iI really think there is much to tht that is why most govrernment oppose the idea of btc, but i hope with time and with the trend of bitcoin if it takes over the world it will overshadow the use of all native currencies. It is the hope of our currency.

This will be unlikely. Because Bitcoin still exists in parallel and depends on Flat. Bitcoin has the ability to dominate the market. Flat still proves it's the number one deal by its convenience and simplicity.