They are indeed opposite, but like heads and tails, opposite of the same coin. Both are payments.

If your neighbor said that he was going to pay a dowry so that his son could marry a his girlfriend, all the neighborhood would understand - except for you. You would seemingly be confused by the matter until you realized that neighbor meant "bride price", after which you would shout from the rooftops (literally) that he meant "bride price". In which case people would ignore you and still say that the groom's father paid a dowry.

Like when George HW Bush said "No new taxes", but pushed for "revenue enhancement". People understood that despite the new label of "revenue enhancement", it still meant taxes.

Or when people move away from cities to avoid "taxes", but end up paying costly Home Owner Association "fees" and end up buying more fuel due to increased travel distances. You could argue that the "taxes" and "fees" + fuel costs are different, but in the end they are the same when your wallet is just as empty.

Even in the case of slavery in the United States, the abolitionists argued that slavery was immoral, while southerners argued that slavery was normal and natural and further argued that Jesus never spoke up against it.
Regardless of the argument, the slave was still a human being that was ultimately unhappy with his lot in life and had no say in whatever fate await him.

It's all really just a matter of semantics and perspectives.