Opera was not always free, you did have to pay for it at one point,
I started using Opera at around version 6 something. It had ad banners that ran at the top and if you paid for opera you could get rid of the banners.
I just ignored them. Soon after, they stopped having a banner version. You do have to pay for a full version of Opera Mobile for cell phones, but Opera Mini is free
The point is that even with banners no one HAD to pay for Opera.