Google hangouts is a wonderful sharing tool from Google+. You can share all with 1-10 people on Google+ Hangouts and keep it private, or schedule a Google+ Hangout on Air (HOA) and share your video with the internet and save it for posterity on your YouTube Channel.
Now with the way Google+ works, every time there is a HOA it shows up on the events page. You can scroll through Events and see watch what people are talking about live.
If you receive an invitation to an event, there is no need to respond via comment. If you're excited and want to express joy in the event great, but it is not necessary. There are option boxes YES, MAYBE or NO. That's fine, pick one for the sake of the of the host, that way they'll know if they can start the event if you're not there. Remember, it's ok to say no. Think of it as a party invite that you need to RSVP to. And if you you repeatedly get invited and you're no longer interested, just send the host an PRIVATE message and ask to be taken off their list, that way they can focus on other people who are interested and want to participate.
BUT by the same token, if you're just going to watch the event (meaning event is Public) there is NO NEED to answer. The host is not expecting you. Yes it would be great if you watched, but if you don't, there is NO NEED to answer. Just keep scrolling until you find something that you do want to watch. It's like watching TV, you don't hit the NO button every time you change channel, you just hit the arrow key. It's hard to put yourself out there like these people are doing, no need making the moderator even more self conscious.