You can say the same thing about any stock, share, gold, silver, precious metals, gemstones, etc, etc. If someone is buying, someone is selling. Is everything a bubble? Obviously not.
that comment puts the whole thing prospective as long as there are people selling you find people buying its a working economy and if the demand of a bitcoin goes you a lot buyers which will buy it on any price and don't wait for the dumper to dump
Because even though no matter how bullish you are on bitcoin, some people are still going to need fiat; probably to pay for bills, to buy random stuff, to pay for some sort of emergency, because they are short on fiat, those stuff. Deal with it, bitcoin isn't used enough(especially in 3rd world countries) that you can live with bitcoin alone. We still currently need fiat to pay most stuff.
unfortunately, bitcoin still haven't reach the point that we can spend just like fiat eventhough i use sometimes like that but you still be needing cash which is still has a huge use cases that cannot be replace yet