One way to take on a human rights activist is by asking him the definition of human behavior. Any society will have some consensus of how to treat each other, most commonly a human rights activist will insist on equality. Then point out the inequality between people. If you have the nerves then you could ask him if he considers the rights of his children as important as the rights of the pedophile who would molest them. If he thinks the pedophile has equal rights then ask him why the pedophile should be locked up then. If he's hardcore humanist he will say the pedophile needs to be cured so he can return to society (in other cases he will say the pedophile needs punishment, if he says that then you've basically won already)
Then point out that even though he might have the best interests for the pedophile he's still admitting that the pedophile is sick and needs treatment until he can be considered equal again. Then point out the differences between cultures, what is considered a pedophile in some cultures is considered normal in others (point out the differences in ages of consent between countries and states, you don't even need to mention third world countries where child rape is common, point out that even in the west in the past was normal for children to marry at a young age)
Now go in for the kill: tell him that the universal declaration of human rights is a western invention. It does not take in account the differences between cultures. The universal declaration of human rights is in fact a form of post-colonial christian racism
. It does not insist equality but it insists sameness and there's a big difference between those two. The declaration of human rights is the democratic west's way of saying "we're right, we're superior, and everybody should live according to our standards" Compare it to the way the west has tried to spread democracy to countries that weren't ready for it (Iraq) or had no desire for it (North Vietnam) Compare it to the different interpretations of honor in different cultures (Japan). By now he will probably have no sound arguments anymore to use against you, the declaration of human rights is a nothing more than a declaration of moral superiority. It is impossible to define what human rights should be on a worldly scale, it should be up to each society on it's own to define them. The fact that it's called a "universal" declaration shows just how arrogant and stupid it is.
In my experience people will either admit that you have a point or they will come up with completely stupid counter-arguments, so stupid that it will probably be safe to just laugh in their face and call them ignorant and full of themselves.
If you want you can skip the part about pedophiles and go straight for the kill. Or replace pedophile with a different example. Read the declaration
and you'll find plenty of articles that are either grossly violated even in the free west or articles that are so vague that there can be many different interpretations of them.