Right, what's the last time you checked the recipients domain MX record before sending an email?
That's just nonsense, nobody does this, people just send mail through some client and never ever check MX records by hand unless they are trying to debug some kind of problem, in fact, the vast majority of people have no clue that something like an MX record even exists. To them email is roughly equivalent to magic.
Perhaps its just the ex-sysadmin in me, but I've done it pretty frequently over the years. Pop open a terminal, host -t mx example.com, done. Mostly I do this when I think there's any chance that my email will get routed to a server in China (pipe the result of the host query through nslookup and eventually to a whois against ARIN to see whether the IP is allocated by APNIC), since I'd prefer to avoid that.
I get that it's not common or simple, but "absolutely no way" doesn't mean absolutely no way that's common and simple. It's doable and, if you want to avoid it, there's plenty of ways to ensure that you never send directly to a Google server.
That's your problem right there. The general population has no way of knowing this, you do, but that's only because of your professional background.
So, for lay people there is absolutely no way and that's the vast majority of them, for us internet techies there are ways but they are moderately involved and too impractical for everyday use. And even then, you've established that you will send your email through google, what are you going to do now? Ah yes, send it anyway.
That's just nonsense, nobody does this, people just send mail through some client and never ever check MX records by hand unless they are trying to debug some kind of problem, in fact, the vast majority of people have no clue that something like an MX record even exists. To them email is roughly equivalent to magic.