Very true. You have to be careful to distinguish between

1) buying patents harms innovation, vs

2) That patent should not have been granted at all.

In my experience, most people arguing 1) either have a very confused argument, or turn out to actually be concerned with 2).

#1 can be a concern if #2 is too common. I.e. if it's too easy to make junk patents, trading them can become a lucrative parasite business. So some will file tons of junk patents just to sell them to trolls. In such scenario the fact that some are ready to pay for such junk encourages more patent pollution which only harms innovation.

Judging by the current patent system, patents and innovation aren't equal in many cases. On the contrary, patents are often equal to the stifling of innovation. So giving money for patents is not equal to giving money for innovation in general case.

I completely agree, but I still see how purchasing patents can encourage innovation.