...and if you look at the tape, he clearly was not resisting after the arrest was initiated.
Furthermore, there were actually no grounds for arrest in that situation.
Before they jumped on him, he was being questioned about selling loosies, which is a quality of life offense that you get ticketed for. The cops were on scene because they got called about a brawl that had already been broken up. When they realized that there was nothing for them to do, Pantaleo started harassing Garner, which he did on a regular basis.
The arrest was initiated because Garner told Pantaleo that he was sick of his shit and wanted to be left alone. Pantaleo jumped on Garner to bring him in "on a humble" for talking back.
Additionally, Pantaleo has more substantiated complaints on his record than most cops on the job with the NYPD and is responsible for the taxpayers taking a hit on three massive settlements stemming from his misconduct.
Eric Garner may not have been the most productive member of society, but on balance, he did much less damage than Daniel Pantaleo has as a cop.