I have attended many meetup groups and have NEVER been scammed. It is a free social service, similar to okcupid but offers more then just meeting singles. After each event members are able to comment and rate the events so if someone wanted to scam you they would have to make tons of profiles to make the group seem legitimate. Read the reviews for the meetup group, view the photo's of the events, contact the venue where the event is taking place. If your afraid of getting scammed (which is crazy) then do your homework to make sure the group is real. It cost money to start a meetup group, you need a paypal account, and members can easily contact the owners of the site to report any problems. This site is a great free service. I have started a meetup group, you pay a monthly fee & it is a TON of work. No one becomes rich for owning a meetup group, there are much easier ways to scam people out of money.
As for the emails you get, CHANGE YOUR PROFILE SETTINGS. It is so easy, I don't receive any emails from meetup.com because my profile setting are set where I don't get promotional emails. Also if you have google, make a social events folder. That way you can view the emails when you want to and they won't be in your main inbox. Meetup is such a great site, not every group is great, but that would be a little much to ask for.