“I wonder,” began the comment posted on my Facebook page last Friday. It was a gentle, almost contemplative start, but it didn’t continue in that vein as ‘David George’ (supposedly of the north pole, Alaska) went on as follows: “I wonder how many of you and your child murdering friends have money invested in arms. Go suck on an exhaust pipe you fucking waste of cum. I hope you die screaming.”

It was pretty standard fare. I didn’t get the photos of dead babies (from those against air strikes) or severed heads (from those in favour) but “murderer”, “blood on your hands” and various other terms of abuse flooded into my inbox. One chap kindly suggested that he was going to drop a Brimstone missile on me – but I didn’t take his threat all that seriously as I’m pretty sure he doesn’t have one.

Yes, there’s nothing quite as unattractive as an MP moaning about his or her lot in life. I get that. We are paid, after all, to take the flak for our decisions and there’s not much point in wanting to be an MP if you faint at the first whisper of disagreement.

I’m glad that the age of deference has ended (if it ever existed). Shrinking violets need not apply. But the reaction to the debate and vote on extending our air strikes to Syria over the last week – the first such vote since social media became pervasive – has shown that for all the positive engagement between MPs and the wider public that the internet affords us, social media are also changing politics in a destructive, nihilistic way that will leave us all the poorer if we don’t take care.

The nub of the problem is that some people seem to think they’re engaging with the whole wide world when they delve into Twitter and Facebook. They suppose they’re listening to all sides of the argument. But all too often they’re actually just seeing a tiny self-selected corner of the world. They follow people they know, they agree with or they respect, so they don’t see the world with all its diversity and difference of opinion. They experience politics in a bubble of their own creation.

So they get steadily more and more certain of their views, more and more convinced in their beliefs and less and less able to admit that there might be another sincerely held, legitimate point of view. They believe that everyone agrees with them, because everyone they follow agrees with them. That brand of personalised conviction becomes self-fulfilling and any challenge has to be fought off in ever angrier terms. When robust argument won’t suffice, personal abuse becomes acceptable and then standard. Thus is bred a form of fundamentalism that brooks no opposition or dissent.

That social media can trap individuals into such a narrow confine is depressing enough, but the effect this has on the body politic is even more disturbing, as the political discourse that this engenders is incapable of nuance or sophistication. It relishes harsh antagonism and detests compromise. Hence, I would argue, the rise of political extremism.

This modern phenomenon also wants to turn MPs into delegates mandated online.

Now, I’ve always thought that Edmund Burke sounded rather arrogant when he told the voters of Bristol that an MP “owes you, not his industry only, but his judgment; and he betrays, instead of serving you, if he sacrifices it to your opinion”. The voters of Bristol thought so, too. They dispensed with his services at the election. But Burke’s point is even more important in an era of social media, when every email, every tweet and every posting comes replete with the demand that an MP should do precisely as his or her constituents wish (which is always precisely as the correspondent wishes).

Last week gave hourly evidence of this, as even though my constituents emailed me on both sides of the argument, those who were opposed to air strikes were absolutely certain that everyone in the Rhondda wanted me to vote against and those in favour thought claimed everyone knew that those opposed were just “terrorist sympathisers”. Incidentally, although people have focused on the self-affirming certitude of the left, this applies across the political spectrum. The balance of the emails I received on same sex marriage, for instance, was overwhelmingly opposed, even though opinion poll after opinion poll told me that the country was heavily in favour.

There are those who see this online democracy as a positive development. They’d like every vote to be subjected to a form of instant online constituency referendum. They could point to Burke again, who said “it ought to be the happiness and glory of a representative to live in the strictest union, the closest correspondence, and the most unreserved communication with his constituents.” In one sense I agree. That “unreserved communication” is even more important today and as an MP it is good to have instant feedback (although the dangers of narcissism are all too clear).

But the job of an MP is also to provide leadership, to exercise his or her judgement, to see each issue against the wider context, to form alliances that can deliver change and to be a forceful advocate. The classic instance is restoring the death penalty. The pollsters tell us this would be popular. Perhaps a majority of my constituents would vote for it in a referendum. But whatever the majority for the death penalty, I would never vote for it, as I have regularly made clear in general elections. If that is the dominant issue for a voter, then he or she should vote for another candidate.

It may sound hideously old-fashioned, but I still think parliamentary democracy is worth fighting for because it is the best way of managing our affairs as a nation so that that which touches all is agreed by all. That means that every vote in the Commons is in some sense a vote of conscience, even if our conscience almost invariably tells us to vote with our party. Of course no MP should treat his or her seat as a job for life and we need greater accountability in our system, but if we just become ciphers for online referendums we shall narrow debate and render our country ungovernable. I even have a sneaking feeling that if Twitter and Facebook had existed in the 1930s MPs under threat of deselection might not have ended appeasement and fought the Nazis.