On our souls:
Many Catholics receive communion while contracepting, meaning that they receive the Eucharist in an unworthy way. This has repercussions on them first, on their soul and spiritual life, and on the whole of society because of the “communion of saints”: our sin does affect the rest of humanity and the whole creation, not just us...

It treats both the man and woman as something less than human.  It forfeits self-discipline and allows them to be enslaved to their desires. It undercuts a full embrace of Christ and his Church.