The Roman catholic church position on scattering of ashes was in the link I gave:
According to new guidelines from the Vatican's doctrinal office, cremated remains should be kept in a "sacred place" such as a church cemetery. Ashes should not be divided up between family members, "nor may they be preserved in mementos, pieces of jewelry or other objects."

The church has allowed cremation for decades, but the guidelines make clear that the Vatican is concerned that the practice often involves "erroneous ideas about death." Those ideas run the gauntlet from deeply nihilistic to New Age-y, the Vatican says, from the belief that death is the definitive end of life to the notion that our bodies fuse with nature or enter another cycle of rebirth.

It's not about preventing the scattering of ashes (for everyone) but of seeking consistency. If you have a Roman Catholic funeral service you should then follow Roman Catholic funeral procedures, not have your ashes scattered in what appears to be a 'Humanist' practice.

Similarly I can't imagine the Roman Catholic church allowing burial in its own consecrated church grounds for someone who had chosen a funeral service under a different faith.

You do get people who choose to follow one practice for the service "It's what mum would have expected" and it reassures her friends and relations, but then scatter the ashes because that's in accordance with their own beliefs.

I can understand the Roman Catholic church's view on this point. (without necessarily agreeing with it)