Because it happens doesn't mean it should or should be permitted to happen in our society. If we kept following the status quo women still wouldn't be able to vote and our current president would be considered 3/5 of a person. If we remove the cloak of anonymity, these sheep, you probably included, wouldn't dare speak your mind as openly.
You've got the attitude right, but the history wrong.
The slave owners wanted each slave to count as a whole person for the purpose of determining the number of representatives each state received (and therefore the number of electoral votes the state has during a presidential election as well). This would have the effect of multiplying the slave owner's vote by the number of slaves he owned, when it came to Federal matters. It would have been like each slave got to vote, but only as their master wished. They'd essentially be voting, by their master's proxy, to keep slavery legal and to keep themselves in bondage. That, quite obviously, is absurd.
The abolitionists (which were dominant in the north) wanted each slave to not count as a person at all, because they were not functioning citizens, and representatives in Congress most certainly did not represent the needs or desires of the slaves. If you're going to say that it's okay to own certain people because of some idea of how they are something less than human, don't turn around and say they're human when it comes to representation. It was a self-serving, cynical argument by the slaveowners to suggest such a thing; "slaves are subhuman so it's okay to own them, but when it comes to counting the number of humans in our state, let's count them, even though they can't vote."
The three-fifths compromise was really a win for the slave owners. The "good guys" in this, remember, wanted the slaves to count as zero fifths.
At no point did anyone say that a slave was three-fifths of a person.
You're also mistaken when you say that our current president would be three-fifths of a person. Our president is from Illinois, and that was a non-slave state. It was slaves that were subject to the three-fifths compromise, not all blacks. Free blacks in the South and North were fully counted.