Google offers free services. People will attempt to abuse them. That's no great surprise, nor is it specific to Google.
When someone abuses Googles services in a way that's a threat to other users there are only two ways to mitigate the incident. The best, by *far*, is for Google to stop the abusive behaviour. The other is for the affected parties to block access to (some subset of) Google. Those are really your only options.
Google is (based on externally visible behaviour) worse at mitigating abuse up-front by discouraging attempts to abuse their service, and at responding to reports of abuse, than other companies - and this appears to be an intentional choice by Google, based on their corporate culture. The tradeoff there is that people are more likely to just block Google servers, in response to the never ending trickle of abusive behaviour.
That's Google's problem. Well, actually, Google don't generally appear to think any of this is a problem at all - and *that's* the real problem as far as the rest of the Internet is concerned.