Jewish society is individualist. Its major tenet is, Do not harm your neighbor, “live and let live.” In the metaphysical realm, the society is bound with the common religious goal of divine service. In reality, the society is bound by communal justice, defense, and charity. Of those, justice is not specifically Judaic, even in Israel. Defense is too politicized, and is an altogether non-Jewish matter in the Diaspora. Charity is the major communal factor among the Jews.
Helping others automatically positions them as neighbors, and binds the individuals into a societal web. Material charity makes stronger ties among people than ethereal ideology. At the current stage of assimilation, charity is critical for the survival of Jewish communities.
Leftism imbues people with guilt. Natural, unavoidable things such as wars, poverty, and inequality are declared evil. People who live safely and prosperously take it as their responsibility to help strangers in distant war zones and less-than-affluent neighbors. Leftist idealists make people sorry for their consumption level. Charity breaks that perpetual guilt. A person who gives the prescribed amount to charity fulfills his societal duty. He can enjoy his means without reservation.
Ten percent charity more than suffices to alleviate extreme poverty. Tithe won’t equalize the people, but biblical charity is only intended to preserve them lives. Biblical ethics allocates charity only to people who positively cannot work, such as—in those times—widows and orphans. They are entitled to minimal sustenance, not to huge welfare benefits.
Rabbis lack a consistent position on charity despite the clear rules set down in the Torah. Traditionally, the tax base of charity is the gross income. That worked in simple economies, but does not work in a complex modern economy in which much of the gross income represents expenses. Many rabbis now demand charity based on net income. The definition of net income, however, is flexible. It depends on the rate of amortization, allowed expenses, and other factors. Rabbis would need their own IRS to calculate tithe on net income.
Treating the tithe as income tax also runs into the problem of the “Law of the land is the law” rule. Jews pay income tax according to the law of the land, and rabbis cannot demand another income tax in the form of tithe.
Ten percent of the net income is, moreover, a fairly large amount. Jews sense that such charity payments are excessive.
The Torah prescribes charity tithe only on basic foodstuffs, not on meat or artisan items. The idea is to redistribute some simple food so that the neighbors do not starve. Presumably, less than ten percent of the population cannot sustain themselves, and tithe suffices. In modern terms, people are obligated to tithe their food expenses, not including restaurant checks.
The biblical rule could be expanded to the current realities to cover other basic needs such as shelter, health care, and education. By analogy with the biblical rule on foodstuffs, people could tithe their housing, medical, and education expenses. Such tithing, though reasonable, extrapolates the Torah rather than follows it to the letter, and could only be voluntary.