"it is sometimes argued" is a perfectly grammatical and acceptable phrase in written English.
You can use it when you want to introduce an opinion or statement that is not necessarily accepted as fact. For example: "It is sometimes argued that the internet has made communication easier for everyone."
In the face of the current financial difficulties, it is sometimes argued that "Europe has lost its compass".
It is sometimes argued that although free trade has some victims, its benefits exceed its costs, so it is possible for its winners to compensate its losers out of their gains, everyone thereby coming out ahead in the end.
It is sometimes argued that deficit spending reduces employment because of fears over the future repayment of the debt.
It is sometimes argued that in such circumstances, policymakers should follow what might be called a decoupling approach.
It is sometimes argued that the surge of nationalism and populism in Europe is the fault of the EU.
It is sometimes argued that rather than Ramadan having a deleterious effect, it actually increases subjective well-being among Muslims.
It is sometimes argued that such language is best expressed in negative terms: God is infinite (not finite), timeless (not in time), and so on.
Central banks have learned to manage the economy so well, it is sometimes argued, that they have more or less abolished the cycle.
It is sometimes argued that the particular disgust at Israel, rather more voluble than that aimed at the Syrian or Russian governments, is further evidence of racism.
It is sometimes argued that innovative technologies would be scarce in a national single-payer system, so we would have long waiting lists.
It is sometimes argued that since our emissions only amount to 2% of the global total, we should relax and wait for the US and China to act.
