Agency work is just soul sucking from a clientele stand point. Most of the companies you work for are massive consumer facing businesses and all you're doing is helping them feed their shit to the public.
This type of work isn't necessarily confined to agencies. The same could be said for several tech companies building products (social networks come to mind).
If you're a technical person there are just far better things you could be working on than agency projects.
You are talking about (philosophical) values. This is a value judgement:
> them feed their shit to the public
A solution to this would be to work for an agency whose leadership and positioning is compatible with your values.
For instance an agency that focuses on clients who sell outdoor equipment for hikers, bikers, gliders and so on would be compatible with the values of someone who thinks it is a good thing when someone goes on a hike.
This type of work isn't necessarily confined to agencies. The same could be said for several tech companies building products (social networks come to mind).
If you're a technical person there are just far better things you could be working on than agency projects.