It took the appeal to emotions of Prof. Farnsworth for the common people to vote positively, by telling that everyone could fall in love in interspecies relationship.
However, we commonly see someone humanoid or biological, most times Fry, interacting sexually with robots. Or Robowhores offering things to a human.
And no one reacts in a bad way, not like the idea would feel skeezy, beyond hiring a sex professional.

So, was robosexuality commonly accepted, except there were interests of powerful people trying to keep it as if the majority feel it's wrong; In order to make the undecided, or those without personal experience would think it's wrong? (We do see that the sponsors for the tv show are religious extremists)...

While Bender does show prejudice, we know he his all kinds of speciesist, so he shouldn't represent society.