I do not have a position on this one way or the other.
But I do have my own story to share.

Having been raised as a Protestant, and truly believing I was in the right, after having been baptized (in the name of the father son and Holy Ghost), I naturally took communion every Sunday.
After some time I stopped attending Sunday services. This would’ve been around 16/17 years old. I am currently 43.
In the decades since then, I had attended a few masses, both Novus Ordo and traditional, when at 18 years of age a priest informed me that I could not take Catholic communion as I was not Catholic (I had taken the communion that day and after mass sought out the priest to ask questions of faith). Since then I had taken communion only 3-4 times knowing it was wrong to the catholic faith, but not having communion was a terrible burden on my soul so I took willingly the wrongness of it. At the times I did I did not know any details of why it was wrong to the Catholic why I should do so. Never, ever, was it my intent to harm anyone else.
Now I have at least a basic understanding of the why it is wrong.
My point is that being out of communion with my savior was so hard that I was willing to take whatever punishment might arise so that I could commune with Jesus.
I hope this makes some sense.

A few years ago, my niece, who was about 13 years old then, and not a Catholic, went to Midnight Mass with me on Christmas eve. She asked if she could take communion, and I said "NO." She then pleaded further and said..."But no one will know..." To which I replied...."God will know." She didn't say anything after that. 
I have difficulty understanding why non-Catholics think that it's alright to take communion. I never had any inclination to take communion before I converted, even though I attended mass nearly every Sunday for two years before converting. 

A few years ago, my niece, who was about 13 years old then, and not a Catholic, went to Midnight Mass with me on Christmas eve. She asked if she could take communion, and I said "NO." She then pleaded further and said..."But no one will know..." To which I replied...."God will know." She didn't say anything after that.
I have difficulty understanding why non-Catholics think that it's alright to take communion. I never had any inclination to take communion before I converted, even though I attended mass nearly every Sunday for two years before converting.

Let me try to answer.  Most "middle-of-the-road" evangelical Protestants believe "the church" is an invisible compilation of those souls truly "saved," known definitely, to God alone.  Therefore, if one says he is a "Christian" and there's nothing to outwardly signify otherwise, then it's fine and healthy to partake of "communion," which, in their minds, is entirely symbolic.  
Liberal Protestants are apt to think likewise.  Some Protestants such as Fundamentalist Baptists, Calvinists, Holiness Pentecostal, etc. wouldn't be caught dead at a Catholic Mass much less take Communion as they believe Catholicism to be idolatrous.  
They are all wrong, of course, but that's the reason.  
An Anglican lady at my workplace once went to Communion at a Catholic (novus ordo) mass when her niece was baptized because "the service was lovely and the priest well-spoken."  She had no idea that she should not have gone.  
I was raised novus ordo, that is, knowing virtually nothing, and went to communion nearly every Sunday, being quite ignorant of the Catholic religion.  I somehow didn't learn the errors, either, just the notion that God is Love, we should love one another, social justice sort of pablum.  At some point, my communion became objectively sacrilegious, because I was eventually doing some things that are mortally sinful. But I had not heard of a mortal vs. venal sin, nor was I knowledgeable of the need for regular Confession.  Nobody I knew went, so I went only once before "first communion" because everyone in the class did, and the teacher told us to go.  The priest came to us, so I went, but gad little to no understanding of what it was or why one should go.  
The fruits of Vat. II!