Two things Wall Street hates are inaccurate guidance and capacity growth by airlines.

United Airlines (UAL - Get Report)  on Wednesday stood before the airline industry and was found guilty of both providing the first and committing the second.

At the JPMorgan transportation conference in New York, lunchtime speaker Oscar Munoz conceded that he could have done a better job informing investors about planned capacity increases so far, but he declined to say that United won't add more capacity.

His remarks came at a time when airline shares are slipping due to capacity growth plans -- with United at the forefront -- combined with a near-industry-wide withdrawal from optimistic first-quarter unit revenue guidance.

Year to date, as of Wednesday's close, Delta shares were down 4%, United shares fell 6%, American and JetBlue shares were down 10%; Spirit declined 12% and Hawaiian lost 13%. The outlier was Southwest, up 9%.

In mid-morning trading Thursday, United was down 2.3%. Most airline shares were flat or lower. 

(Note to Warren Buffett: Are you sure you want to come back to the airline industry after staying away for a quarter century?)

At the conference, JPMorgan analyst Jamie Baker told Munoz that he understands: "You were punching below your weight in certain places like Chicago," and you may have needed to bulk up a little.

 "What investors failed to hear today {is that} this is a one-time catch-up effort," Baker said. "It's the potential perpetuity of increased capacity that has people worried. A one-time adjustment, that's fine. You fix it and you move on."

But Munoz, given the opportunity to make nice and embrace Wall Street's dream of airlines that don't grow capacity, rejected it.

 "We just brought in a network expert," Munoz said. "In a network our size, there's always going to be opportunity. "

Thus, "I cannot tell you anything is one-time," Munoz said.

Munoz was speaking after United had already revealed, in slides prepared for his presentation, that it will boost full-year 2017 consolidated capacity growth to between 2.5% and 3.5%, up from previous guidance between 1% and 2%.

Domestic capacity will grow between 3.5% and 4.5%, up from guidance between 1.5% and 2.5%: international capacity will grow between 1% and 2%, up from 0.5% and 1.5%, the slides showed.

In a note following the presentation, Baker wrote, "United is focused on bolstering its domestic network after several years of a declining footprint and reduced competitiveness.

"Unfortunately, United's efforts to allay mounting investor concerns regarding growth were not as strong as we had hoped," Baker said. "A best-case scenario would have taken the form of 'that's it, we're done, this is a one-time adjustment.'

"Instead, United left the door open to further capacity growth should margin goals fail to be achieved, a fact that may pose further challenges to UAL and sector fundamentals, to say nothing of near-term investor sentiment," he said.

On Thursday, in a somewhat disapproving note, Evercore analyst Duane Pfennigwerth downgraded United to inline from outperform.

The carrier is "abandoning its commitment to shareholders to keep its capacity growth below GDP," Pfennigwerth wrote. Moreover, he said, it revealed its growth plans by announcing new routes in a schedule change announcement, rather than by disclosing an upward revision to its guidance.

Nevertheless, he said, "Our rating change has nothing to do with how United's higher capacity growth was communicated but rather the network planning decision itself.

"While there may be numerous practical company specific reasons to increase domestic capacity growth plans by 200 basis points following softer industry revenue trends YTD, it demonstrates a lack of focus on long-term investors' primary concerns," he said.

 Speaking for much of Wall Street, Pfennigwerth continued: "We prefer when high unit cost legacy carriers fund growth opportunities with offsetting cuts to underperforming segments of their network."

And a little jibe here: "Given United's low relative margin position, we're confident these funding opportunities exist (777's flying domestic?).

"Investor sentiment for airlines is always fragile," he concluded. "Consistent effort is required to build and keep investor trust.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.