I think it’s pretty clear that it just depends on who is doing the inviting and your relationship with them. To ignore someone is rude, in social media or ever. If you care enough, you won’t let them think that is what you are doing. If I don’t want to go and it is someone close to me, I just say “Sorry, I’m not going to make it. Thanks for thinking of me”. Unless it is my Mom, I don’t usually get asked why. That would be rude too.