Ideally, there would be no need for charity. But in a world of inequality and vulnerability, private donations can mean the difference between life and death, dignity and humiliation, or subsistence and sustainability.

But even when it comes to charity, not all causes are created equal. Contrast, for instance, the global generosity following the 2004 Asian tsunami with the trickle of funds in the wake of the recent floods in Pakistan.

Some of the most effective fundraising occurs for objectives that I and many others would not define as charitable and for causes that are already so flush with cash it leaves you wondering why they need more.

Take the Israeli army. At a single glitzy charity gala in New York earlier this year, an impressive $20m (£12.5m) was donated in one evening by the rich guests. This event was organised by Friends of the Israel Defence Forces, the main US organisation raising funds for Israeli soldiers on active duty, which raised nearly $50m in 2008. Similar fundraising operations exist in a number of European countries, as a recent investigation by the Inter Press Service revealed.

With Israel possessing the most powerful military in the Middle East and one of the richest and best-equipped in the world, many will be scratching their heads as to why the IDF needs "charity". Not only are soldiers the responsibility of the army they serve – and by extension the government – surely the IDF can afford to take care of its own. After all, it swallows up at least 6% of Israel's GDP and receives some $3bn a year in US military aid. It is high time that Washington converted this to civilian aid and made it conditional on progress towards a final peace settlement.

Moreover, there are numerous ethical objections to defining this kind of fundraising as charity and exempting it from taxes. Despite its name, the IDF is not just about defence, it is also about attack, unless you happen to believe that attack is the best form of defence.

Although Israel has the right, like any other country, to possess an army, its military is involved in an ugly occupation, regularly invades or mounts incursions into neighbouring countries and territories, and some of its soldiers commit human rights violations and even war crimes. One way to ensure that taxpayers do not become unwitting accomplices would be to remove the tax exemption of organisations raising money for foreign militaries or soldiers by not allowing them to register as charities.

But even if the IDF were, as it claims, "the most moral army in the world", should it or other militaries even be allowed to fundraise abroad?

There is a case to be made for outlawing charities whose purpose is to serve foreign militaries. One reason for this is that there is no guarantee that the money raised won't be used to commit human rights violations or potentially reward individuals who have committed war crimes – which would compromise the fundamental legal role of charities to serve "the public benefit".

Some are bound to protest that organisations such as Friends of the IDF are not raising funds for the army itself but for the social, cultural and economic wellbeing of its active soldiers. But this is a disingenuous argument: by removing some of the burden of caring for soldiers, these charities not only indirectly enhance the readiness of an army, they also enable the state to divert more of its own resources to purchasing arms and other combat-related activities.

Another reason is that it is not inconceivable that foreign armies receiving tax-free charitable donations could compromise the national security or undermine the foreign policy of the donating country, not to mention threaten regional or global stability. Navigating the minefield of deciding which armies are "worthy" charity cases is not only incredibly subjective, it can also potentially backfire.

While charitable activity targeted at armies, especially those of allied powers, falls into a somewhat grey area, charitable activities that contravene international law and the government's own legal position are more clear cut. Yet numerous charities, from Christian evangelists to pro-settler Jews, support illegal Israeli settlement activities. The New York Times identified at least 40 American groups that have collected more than $200m in tax-deductible gifts for Jewish settlement in the West Bank and East Jerusalem over the past decade.

Despite the questionable nature of the pro-IDF and pro-settler organisations mentioned above, we must not forget nor lose sight of the fact that Jewish charities and civil society organisations raise funds for numerous worthy causes and we can learn a lot from the solidarity Jewish communities around the world show one another. In addition, many Jews, particularly progressive ones, are actively involved in fundraising and volunteering for many non-Jewish causes, as well as activities aimed at improving the lives of Palestinians living under occupation.