That was his choice. He could have chosen the legal avenue and would have been afforded whistleblower protections. Fleeing the country with classified material doesn't afford you protection.
Copying from another comment, to prove how stupid is to expect that a secret service will pet you on the head for talking out against them:
"Thomas Drake did everything you say is the right, he paid the price:
| The first is Thomas Drake, who blew the whistle on the
| very same NSA activities 10 years before Snowden did.
| Drake was a much higher-ranking NSA official than
| Snowden, and he obeyed US whistleblower laws, raising
| his concerns through official channels. And he got
| crushed.
| Drake was fired, arrested at dawn by gun-wielding FBI
| agents, stripped of his security clearance, charged
| with crimes that could have sent him to prison for
| the rest of his life, and all but ruined financially
| and professionally. The only job he could find
| afterwards was working in an Apple store in suburban
| Washington, where he remains today. Adding insult to
| injury, his warnings about the dangers of the NSA’s
| surveillance programme were largely ignored.
I'll have to read more but it seems that he didn't use proper channels he went to a reporter (with only unclass material, he claims). They raided him probably expecting classified material to be involved. Thanks for sharing, I hadn't heard of this instance.