Mandatory community service would help increase the standard of living for the poor. A couple of hours required service each week, or required donations of food or money, from each citizen requires little effort from each person but results in improved services for the poor and extra support for the lower classes to supplement government aid.
People should not be ever required to help the poor. Many people believe that they are entitled to keep the money they earn, and they should be allowed to do so. Given that there is already a strong safety net for the poor provided through taxes, then any other charitable giving should be left a personal freedom, not a responsibility
While helping the poor is a moral and worthwhile endeavor, nobody should be forced to do so. It's within our human rights to spend our money however we want to. While governments can start initiatives that give people opportunities to help the poor, nobody should be forced to do so against their will.
It is already mandatory for people to help the poor through taxation. Whether or not they choose to contribute further through personal contributions should be a personal choice. Some people simply cannot afford to help the poor beyond the money they are initially taxed. Helping the poor is a reflection of compassion and generosity. To be forced to do it begrudgingly detracts from the kindness of it.