Why would a group of pro-abortion protesters walk into a church and interrupt a mass?
Here's one reason, and what I believe is the likely one: they want to be threatening. They want to put out the impression that, if you don't agree with them, they may show up at your church - or maybe your place of work, even your home - and make you feel threatened. And if you're threatened, maybe you'll stop opposing abortion. Maybe you'll shut up and give them what they want. And if you don't, well, maybe they need to make the message get across clearer.
On that note, it's a good time to familiarize yourself with the concealed carry laws in your state. The fact that this protest took place in Chile should do nothing to make anyone feel relaxed.