I'd appreciate it if ycombinator would pull their ads from Breitbart. Thanks

Put ads on breitbart? You seem to be very much missing the point.

Edit to add: Even if you believed, for some reason, that you could usefully engage the readers of that site, giving money to an organization whose goal is to spread beliefs that are apparently abhorrent to you would be a questionable plan. At the same time as you would be spending money to promote your beliefs, you are funding the opposition.

I think you'd need to provide some evidence that by commercially funding a view you really don't like, support for that view is reduced. I would expect the opposite to be the case. Why do you think it would work?