I fail to see anything in the least irresponsible about grazing an animal on public or otherwise ungrazed land.

Read the article which your linked page refers to. Quite apart from animal welfare issues, flygrazing is a problem because it interferes with the lawful use of the land, creates problems with neighbours and can present safety hazards especially when close to roads or paths.

I am the land manager for a national charity which owns land throughout the UK. From time to time we have had fly-grazing on our land, and on no occasion was it done by gypsies or travellers. Previously it was difficult to take action, and expensive. This new law is to be welcomed.