With Mohamed Morsi and his Muslim Brotherhood distrusted by secularists, order and political life is breaking down in Egypt

Hopes for a swift end to Egypt's impasse faded on Monday as opposition leaders rebuffed a call by President Mohamed Morsi for a "national dialogue" amid violence that cast a long shadow over the second anniversary of the revolution that overthrew Hosni Mubarak.

Fifty dead, hundreds of arrests, curfews and a state of emergency in three provinces were stark reminders of the volatile standoff between Morsi's Islamist and conservative supporters and secularists, liberals, left-wingers and Copts.

Extreme polarisation is the hallmark of a transition whose outcome remains unclear. Police firing tear gas to disperse demonstrators on Cairo's Qasr al-Nil bridge on Monday was a case of deja vu – exactly two years to the day since the coercive power of the Egyptian state first seemed to have been lost when the headquarters of Mubarak's ruling National Democratic party was burned down.

Continuing distrust of the powers-that-be was starkly evident in weekend fighting in Port Said, a battle-hardened city where violence erupted as relatives tried to storm a prison housing 22 football fans who were sentenced to death over last year's stadium stampede disaster.

It is a measure of just how bad things are that even before an angry Morsi spoke to the nation on Sunday he was taunted that as the Muslim Brotherhood candidate in last summer's presidential race he had pledged never to impose a state of emergency. The Brotherhood, in turn, blamed the opposition National Salvation Front (NSF) for "chaos and thuggery" – ignoring the substance of its complaints since Morsi took office last summer vowing grandly to rule "for all Egyptians".

No surprise, then, that the NSF's Mohamed ElBaradei so quickly dismissed Morsi's dialogue call as "unserious". Unless Morsi agreed to a national unity government and a commission to amend the constitution then the next presidential elections due in 2016 should be brought forward, he said.

Morsi was always going to face objections to the narrowness of his victory and mistrust of the Brotherhood – the legacy of its Islamist ideology and decades of being forced to operate in a semi-underground manner. But the row over the new constitution, his sweeping presidential decrees, generally poor performance and a disastrous economic situation have used up what little credit he had at the start.

"Down the path of the Muslim Brotherhood's unilateralism, plus incompetence, lies instability," was the pithy conclusion of the political scientist Michael Wahid Hanna. "This approach simply can't work during what is still a time of transition."

But the opposition is under fire too, accused of incoherence and opportunism. Hinting at a readiness to boycott the next parliamentary elections when polls show steadily declining support for the Brotherhood's Freedom and Justice party looks simply self-destructive.

Alarmingly, there are signs in this febrile atmosphere of a proliferation of "militias", whether the anarchist Black Bloc or Salafi activists with roots in the once-terrorist Gama'a Islamiyya. "Ultra" football fans may just represent themselves but their confidence attests to a breakdown of order as well as the fragmentation of political life. It will be worrying if too many Egyptians come to believe that it is simpler or easier to decide their country's future in street battles than by voting.

Pessimists fear an unstoppable dynamic that generates repression, chaos and instability – each side feeding on the other's excesses and miscalculations.

But there are more benign scenarios too. "Consensus, for all the hurdles it must overcome, remains the most likely way out," predicted Steve Negus on the Arabist blog. "For all its political polarisation, Egypt still has a genuine abhorrence for violence that makes a civil war unlikely – for now. The experience with one dictatorship means that the country may be reluctant to go back to another, and this makes a coup unlikely – for now."

There is no guarantee that things will stay that way. "Every year in which the protests continue, traffic is paralysed, the pound devalues, and voters shake their heads at the flames and bodies on their television screen increases a public desire for some resolution, any resolution, at whatever cost," Negus wrote.

"More widespread violence or a return to military rule, currently barely imaginable, may become real possibilities. This spectre, the more likely it becomes, will bring Egypt's factions to work together to rebuild state authority. They still have some time."