That would depend upon their convictions. We do not judge Protestants on principles they do not hold. If they think one religion as good as any other, I suppose they could attend almost any religion with a good conscience. But if an Anglican, for example, thought his to be the only true Church, and that all others were wrong, he wTould sin by attending other forms of worship. Objectively, of course, a Protestant does not sin by attending Catholic services. One who has the wrong religion may attend services of the right religion. But he who has the right religion certainly cannot attend the services of a wrong religion. Catholics may not assist at any but Catholic services.
Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer CartyBoost your faith with the help of the Catholic book we suggest below. It is a helpful resource that answers a lot of questions and can be shared with family and friends.
The Case for Catholicism - Answers to Classic and Contemporary Protestant Objections
Disclaimer: This post may have affiliate links, which means that if you decide to buy something after clicking on one of our links, we will get a small commission at no extra cost to you. Thank you.