Samuel Kemp, Piper Jaffray: "We see this as the right long-term decision."
When people are selling the stock, they're thinking: "This could lead to reduced Facebook engagement, ad impressions and therefore ad revenue," according to Kemp.
But Facebook still owns Instagram, and that could absorb any ads that don't find a home on Facebook's main product, Kemp wrote. Plus, Facebook has proven its ability to charge more for ads in the past.
Overall, Kemp wrote that he didn't see enough evidence of advertising impacts to change his long-term view of the company. Indeed, the changes could combat user attrition over time by making the product more pleasant, he theorized.
"We see this as the right long-term decision for the platform and, over the near-term, doubt that this will have a material impact on revenue," Kemp wrote.
Brian Nowak, Morgan Stanley: Be cautious; there are "just as many unknowns vs. knowns."
Nowak urged caution in his note, writing that there were "just as many unknowns vs. knowns" about the company's future.
While Zuckerberg's post "injects incremental near-term uncertainty," Nowak noted that the overall trend toward "societal interaction" has been pretty consistent since mid-2017. Facebook may even have already been testing these changes over the past year, he said.
Given Facebook's growth on other platforms, such as Instagram, Nowak maintained that the stock wasn't expensive.
Brian Wieser, Pivotal Research Group: "[W]e think the actions the company will take pose a headwind to growth."
Wieser is a rare Facebook bear, and maintained his "sell" rating on Facebook shares on Friday. But that's not necessarily due to the changes announced by Zuckerberg, he wrote.
"In short, we think the actions the company will take pose a headwind to growth for the business in the near-term," Wieser said. "However, we also think that the actions taken will be helpful for the long-term health of the overall business."
Instead, Wieser said he is tracking Nielsen data that indicates Facebook usage was already falling prior to this announcement, "if from very high levels." The decline was slight, but Wieser noted that Facebook may actually address the root of that decline by cracking down on concerns such as so-called fake news.
Wieser also said that Facebook has plenty of other near-term challenges, such as swelling content costs, regulation and changes in ad policies and metrics.
Justin Post, BofA Merrill Lynch: Keep an eye out for engagement numbers.
Even if Facebook users spend less time on the platform, Post noted that it will be tough for investors to know.
"Facebook has not disclosed an average daily time spent metric in several quarters and visibility is limited to management disclosure," Post wrote. "The metric question is if Facebook will see lower daily usage from the change, which would show up in reported daily active users (DAUs). ... We think some investors will view this as the "right" move for the long-term health of Facebook, but management may need to better outline drivers of core Facebook time spent from here."
Post said that his checks on fourth-quarter Facebook advertising have been positive and said Facebook's new video platform, Watch, could prove a new opportunity for publishers and advertisers.
But, he noted, "Watch still needs a hit 'viral' show to really get users attention, in our view."
Scott Kessler, equity analyst at CFRA Research: Bad short term, but good for "brand value."
"FB is prioritizing quality over quantity in terms of content and advertising, which we think could have a negative impact on revenue, especially over the nearer term. However, we see these changes as constructive for brand value," Kessler wrote.
Daniel Ives, head of technology research at GBH Insights: It's still a global growth story.
Ives said he is not worried, because Facebook has "strong monetization tailwinds" in 2018, thanks to its massive monthly active user base.
"Facebook will continue to grow its massive global installed base in our opinion while importantly monetizing users especially on the Instagram side of the house, which remains the 'core 1-2 punch' that underlies our bullish thesis on the name," Ives said in a note released late Thursday.
Ives raised his price target from $210 to $225 — a nearly 20 percent increase from Thursday's close.
— CNBC's Arjun Kharpal contributed to this report.