In some private discussions with ex-JWs over the years, I have boiled down some of the disagreements to a different view of what worship is or is not. This view often unwittingly affects ex-JWs, and underpins their arguments, even though they do not realize it.
To a JW, worship of Jehovah is done by going out door-to-door, attending meetings, commenting, singing, and prayer. These are acts only done to and for Jehovah.
To a Protestant, going door-to-door is nice, vene being at Church is nice, but not worship. Singing and prayer are acts of worship, particular what is said to God (the Father, the Son, and the Holy Spirit).
To a Catholic, prayer of itself is not worship, because one can talk to the Saints who have passed on to Heaven, which include St. Mary, Mother of Jesus Christ. However, celebrating Mass, with the ritual and singing and the type of prayers to God are worship.
So, when a JW leaves the Watchtower Society, they often carry with them this concept that any prayer must constitute worship. Thus, ex-JWs will insist that Catholics worship Blessed Mary because they talk to her in prayer ... or that Catholics are bad because they talk to other Saints or dead relatives. yet, for Catholics, communion with the Saints is actually part of the confession of faith that dates back to the first century ... (one can find this in various forms of the Apostle's Creed).
I am not suggesting that Catholics are right or worng in this ... but that the basic paradigm is often a cause of disagreement because ex-JWs fails to completely drop Watchtower paradigms as well as they through they did ... and Catholics, like most Protestants, do not care to really understand JWs.
Jim Whitney