I have a slightly different take on this. Let me explain. I would add, though, that I am a trial lawyer; love engaging in off-the-cuff debates with people like JWs; and find those sort of experiences fun: 3 months ago I got accosted by an anti-Catholic Seventh Day Adventist; I had such fun with him, he fled!.
I really, REALLY think it’s extraordinarily disrespectful and insulting for the JWs to do what they did, namely, drop the bomb that the “Mass makes no sense” at a time when you are trying to leave, and I’d tell them so in no uncertain terms.
I’d be tempted to ask them: * How would you like it if I walked up to you, said “the Watchtower magazine [the JW rag] is valueless claptrap,” then tried to just walk away? *(“Because it is, of course!”) How about if there were 2 of me and I took on 1 of you (which these folks do deliberately)?
These folks use the tactics they do because they want to out-debate you; they want to make you uncomfortable; and they expect to do so. They are not generally, “our friends in Christ,” although they act that way – if they were they wouldn’t resort to the “insult” tactics.
Also, I find that these folks are often anywhere from unsteady to completely unprepared for any sort of pushback. I might ask them something like: There are a few thousand JWs worldwide and over a billion Catholics, and we’ve been around a lot longer…if we’re wrong, are you suggesting God would mislead so many people worldwide? There are 32,000 sects of Protestantism worldwide, all of whom claim to have the truth – why are you correct and the 1.2 billion Catholics – who gave the world the Bible, not the other way around – incorrect? These folks are generally unprepared for this.
IMHO, NEVER let JWs, Mormons, etc., talk about what they want to. They’re very rehearsed. Talk about what YOU want to, and watch them flounder.
That said, these things take a lot of nerve and it’s not for everyone. I have no idea how old you are or the circumstances of this encounter, so please – I think you did fine. Just some points to ponder when they come a-knockin’ again…