In brief remarks to the nation yesterday on the Boston Marathon bombings, President Obama said that "we all have a part to play in alerting authorities. If you see something suspicious, speak up." In Washington, D.C., electronic signs urged commuters to be on guard. Law enforcement, big-city mayors and security experts all echoed that famous post-terrorism refrain: "If you see something, say something."

But who really means it?

In post-9/11 America, the truth is that our politically correct guardians only want you to see, say or do something if it can't be construed by grievance-mongers as racist, sexist, Islamophobic, homophobic, nativist or any other "-ist" or "-ic."

Face it: We live in a self-defeating culture that pays lip service to heroic action in times of crisis, yet brutally punishes the very kind of snap judgments and instant security profiling that make such heroism possible in the first place.

Just take a look at some of the caustic reactions to citizens and watchdogs who stuck out their necks during and after the Boston Marathon bombings. A quick-thinking spectator at the race reportedly tackled a 20-year-old Saudi Arabian student visa holder he believed was acting suspiciously. The student is not considered a suspect at this point, but remains a "person of interest" in the case. The student's home was searched Monday night in Revere, Mass., by a phalanx of law enforcement agencies.

Time magazine correspondent Michael Crowley clucked: "It'll be a real shame if a Saudi guy was tackled and held simply for running in fright -- and for being an Arab." Music producer Sledgren took to Twitter to bemoan "prejudice America." Indian television anchor Gargi Rawat called the civilian's actions "sad." Gawker editor Max Read declared: "(T)his poor Saudi kid should sue the guy who tackled him."

For what? For taking all those "See Something, Say Something" ads seriously? Hang him!

If the Saudi student tries to sue, we already know who will provide legal aid and comfort. In 2007, when passengers reported concerns about a group of rowdy flying imams, the Council on American-Islamic Relations threatened to sue the unnamed "John Does" who went to authorities. Thankfully, Congress passed legislation protecting whistleblowers.

As GOP Rep. Bill Shuster said at the time: "No American should ever be sued because they tried to stop a terrorist act. No American should be forced to second-guess a decision to alert authorities that could save the lives of others."

Nobody knows what's going on behind closed doors as the current bombing investigation continues, yet media scribes, foreign journalists and social media sideliners are convinced: The tackler is racist. Anyone who mentions the nationality of the tackled student is racist. Forget terrorism. RAAAAAAACISM is the real homeland security threat to our nation.

The same unserious response greeted anyone who breathed public mention of the fact that the Boston Police Department issued a BOLO alert Monday afternoon for a suspicious individual. Investigators warned police officers to be on the lookout for a "darker-skinned or black male" with a "possible foreign accent."

Incredibly, BPD got blasted for issuing an alert that was both too broad and too specific. "That's all of Boston," one critic carped. Others protested disclosure of any descriptive details. A common retort: "Why?"

Why? Well, if we're all serious about bringing the killers and their conspirators to justice, it kinda helps to know what they might look like. Just saying.

The Shut Up Brigade struck again after a U.S. Airways plane at Boston's Logan Airport was evacuated Tuesday because of suspicions about two passengers seated apart and speaking Arabic. "Racist paranoia," blogger Shymala Dason decried. "Ugh," wrote Newsweek social media editor Brian Ries. "This is ridiculous," fumed Arabic language educator Jinanne Tabra.

Ridiculous? Tell that to shell-shocked marathon runners and their families traveling home after the Boston terror bombing. They were the ones on the plane, at the very airport where Arabic-speaking 9/11 jihadists hijacked two flights and brought down the Twin Towers. I won't second-guess any of them or the bystanders who tackled the Saudi student -- because I have not forgotten.

I still haven't forgotten the passengers and crewmembers who tackled al-Qaida shoe-bomber Richard Reid on American Airlines Flight 63 before he had a chance to blow up the plane over the Atlantic Ocean.

I still haven't forgotten Brian Morgenstern, the teenage Circuit City worker who contacted authorities in 2007 when suspicious Middle Easterners brought in tapes of themselves shooting off guns and shouting "Allahu Akbar." The men were convicted of plotting to kill American soldiers at Fort Dix.

I still haven't forgotten the alertness of actor James Woods, who notified a flight attendant that several Arab men sitting in the first-class cabin on an August 2001 flight were behaving strangely. The men turned out to be 9/11 hijackers on a test run.

Hindsight hypocrites will only give you immunity from public excoriation if you can guarantee in advance that your fears or suspicions are 100 percent right. And no one can.

To hell with the "See Something, Do Nothing" cowards who sit on the sidelines wielding their "racism" and "Islamophobia" cards in the aftermath of every terrorist attack. I would rather be damned if I do than dead if I don't.