"Because Ephraim has multiplied altars for sinning, they have become to him altars for sinning. Were I to write for him my laws by the ten thousands, they would be regarded as a strange thing." - Hosea 8:11-12 ESV
For political reasons Ephraim set up many places for people to make sacrificial offerings but those places just became places where the people 'fell short' over and over again.
An altar is a place where religious ceremony is carried out. A sacrifice is made there. It is not a practical place for the person making the sacrifice. No food is made there, no money is made and nothing is learned. You bring something and leave it there to assuage your guilt.
"As for my sacrificial offerings, they sacrifice meat and eat it, but the LORD does not accept them. Now he will remember their iniquity and punish their sins; they shall return to Egypt." - Hosea 8:13 ESV
The priests however do profit from the altar. Portions of the meat brought to the altar are what fed the priesthood. More sacrifices meant more meat.
This whole thing was not pleasing to God. Because of the emotional rebellion of the priesthood bowing to politics for personal gain God would usher a return to bondage for the whole system.
The cross is our one altar and it was outside the religious system. Romans crucified Christ under pressure from the Hebrew religious system of the day who was forbidden to execute criminals. But, On a deeper level God was sending His Son to die for sin. Jesus became sin. All of the sins of the world past, present and future were placed on Him and in one very unceremonious act sins were paid for.
"But when Christ had offered for all time a single sacrifice for sins, he sat down at the right hand of God, waiting from that time until his enemies should be made a footstool for his feet. For by a single offering he has perfected for all time those who are being sanctified." - Hebrews 10:12-14 ESV
Do we have many altars or just one?
Our many altars just become places where sin is multiplied. People deal with guilt in many complex ways giving and doing all kinds of things as a way to feel better about themselves but God only has one altar. It is a rough hewn wooden cross that stood unceremoniously outside of Jerusalem's walls where a Savior gave His life.
Tear down your altars if you have them. They are worthless places that just usher a return to previous bondage.
It is finished and Christ is alive. We don't get our sustenance from the meat coming off the altar we commune with the blood and body of our once and for all sacrifice. It is free from all political or economic attachments. We live guilt free among a people that live guilt free. Ten thousand subtle rules and guidelines could never produce that in our lives. One Savior on one cross setting us free is what made that happen.