As a networking engineer using a VPN service where you don't have any information on the other end of the tunnel or worse install software which can essentially packet mirror your traffic to any location is the worst possible idea and I can't believe they convinced so many people to do it.
The trust in the unknown systems of the VPN provider may still be better than the known practices of your local ISP/government though. You shouldn't necessarily rely on it too heavily but it's good to have the option.
While those are valid concerns, it's not really hard to see why people use VPNs. Just look at how companied and countries abuse the internet, abuse us.