Why does Google Chrome allow extensions such as AdBlock?

[Lorenzo]

...when Google itself depends on advertising revenue to stay afloat?

AdBlock is currently the most popular extension for Google's Chrome browser. Unlike Firefox which is controlled by the Mozilla Foundation, Chrome is controlled by Google which depends on advertising revenue in the form of their AdSense advertising network. They also own YouTube which also uses AdSense for ad revenue. The AdBlock extension allows those who have it installed on their computer to block banner ads and text ads as well as those on Facebook, YouTube, and Hulu.

Anyone know the reason for this? One answer that I found on the web is that Google used to not allow any third-party extensions. But this made their browser unpopular so they decided to change their policy and allow them and that it's because of this that extensions such as AdBlock are allowed to exist. But couldn't they just selectively block AdBlock while allowing others to continue making third-party extensions that don't affect their profits?

[NyeFe]

Every other major browser vendor who does not depend on ad revenue, provide Adblock.
If it's remove by Google, then users will simply switch to browsers such as Firefox, Opera... Who do provide it
So this would mean they will lose their market share to competitors

[Lorenzo]

Every other major browser vendor who does not depend on ad revenue, provide Adblock.
If it's remove by Google, then users will simply switch to browsers such as Firefox, Opera... Who do provide it
So this would mean they will lose their market share to competitors

So the negative financial impact of people not using a free browser outweighs the positive financial benefits of increased ad revenue from the percentage of people currently using Chome with AdBlock who will suck it up and continue using Chrome even with AdBlock disabled by Google? If the browser is free then wouldn't the negative financial impact be small, if it even exists at all?