Fears of the "B"-word (bubble) are growing louder. There's a staggering split screen: a teetering economy with millions unemployed in a pandemic that's killing thousands per day and newly public tech companies riding high on nosebleed valuations.

Yes, but: Investors acknowledge the backdrop is bad. They say investors are piling into and betting on companies like Airbnb and DoorDash for better times ahead.

What they're saying: “The public markets have adopted a venture mentality,“ Joe Kaiser, a director at Mercato Partners, said during an Axios event earlier this week.

• Investors are thinking about what a company like a DoorDash can do five years from now, Kaiser said. “That's why we're seeing valuations that look frothy," relative to the economic backdrop.

The other side: The soaring valuations show "the extreme exuberance and unprecedented liquidity in the market," James Gellert, who runs financial analysis firm RapidRatings, told the New York Times.

Airbnb's valuation is now roughly $86 billion —  a big leap from its $18 billion valuation in April, when the company took a huge hit as the pandemic rocked the economy.

DoorDash was last valued at $16 billion by private investors — but as of close yesterday, it's worth over three times more than that.

One more: AI software company C3.ai went public this week — priced at $42 per share (already higher than its upwardly revised IPO range).

• It opened on Wednesday at $100 and finished 120% higher. Yesterday it closed up another 40%.

The buildup: Earlier this week, there was record volume in the main IPO exchange-traded fund — which swaps in new, sizable public companies shortly after they debut. (The ETF is up about 3% so far this month, following its best monthly gain ever in November.)

The big picture: Stock market investors' euphoria over these tech stocks is another manifestation of the risk-on mentality that's ballooned even more in recent weeks, as the possibility of a vaccine and a return to normalcy appears on the horizon.

• Plus: "You just have this worldwide phenomenon of capital infusion, money printing, low interest rates — where capital is being forced into equities markets," said Arjun Sethi, co-founder of venture firm Tribe Capital.

The bottom line: If the companies can't keep up with public market expectations, "you could see some carnage pretty quickly," Kaiser said.