Ah, 3/5, slightly better then

Still declares them "legally" to be less than a person.
That was an anti-slavery provision.
Independance from Britian would not have been possible without all, or at least most, colonies cooperation, including the slaveholding ones. Slavery was very much a "civic" which contradicted the values the early Americans were trying to form a country around, but that doesn't change the fact that many of the people at the time (in the southern colonies like much of the world) relied on slaves and wouldn't give it up easily. (NOT an excuse, of course, just stating what the founders had to work with)
But they knew they wanted to lessen the spread of slavery, and to restrict it. If they could do so without a war (which ultimately the could not, but they of course wanted to avoid a war between colonies in the future) they would need to give more influence to free states than to slave holding states, right?
Slaves could not vote. Counting a slave as a whole person
for purposes of representation would not mean that they got any more rights or recognition, just that the poeple chosen by their "owners" (and thier neighbors, since of course most southerns didn't own slaves) would get more power in congress. That's the key, the "3/5 provision" was a compromise designed to
weaken the slave holding states power.
The constitution was not easily written, but it is the oldest constitution in effect today. The founders did not want to make war among themselves (or split up to allow european powers to reassert control) immediately after the revolution, so they made thiscompromise.
Of course, the supreme court did call all blacks basically non-people in the Dred Scott case, briefly ensrining that into US federal law, but also outraging huge numbers of people and was part of the impetus toward civil war.