Crowd-sourcing has been often regarded as something that can be very harmful to business. Advertising agencies would not be exempt from this. If they were to experience more crowd sourcing then they would very likely see harm done to that side of the business. This is why crowd-sourcing has the ability to hurt the business of advertising agencies.
Crowd-sourcing could easily hurt the advertising agencies, which isn't necessarily a bad thing. New technologies come along and either increase efficiency or provide a more effective way of doing a job. Ad agencies still provide a valuable service to some larger clients, but crowd-sourcing can be very beneficial to others.
I do not believe that companies have learned the true potential of crowd-sourcing and for that reason I do not believe it has hurt the business of advertising agencies. Honestly, even if crowd-sourcing did win favor, I don't think it would harm these agencies. I believe crowd-sourcing only sends out the simply tasks.
Look around you. You can't watch a video anymore without seeing an ad. You can't open your email without seeing an ad. There is so much advertising being thrown in our faces on an hourly basis it's sickening. Advertising agencies don't need to be worried about in this society. The brain rot and consumerism they cause needs to be worried about.
Crowd-sourcing does not hurt the business of advertising agencies. It gives the business more time to focus on other tasks to propel their companies forward. They can also reduce their expenses this way and increase their profit margins. It seems to have advantages for everyone and they can focus on the advertising if they need to.