The US Constitution establishes a separation of Church and State. This doesn't mean that the State need to divorce itself from any reference to God or morality, but it means that the Federal Government must not interfere with the free expression and practice of religion.
Both welfare and marriage are establishments and institutions of religious practice. James 1:27 says that pure religion involves the business of visiting the fatherless and widow. Welfare is the business of religion. That means federal social welfare programs encroach upon and usurp the rights and duty of religion in violation of the First Amendment. Additionally, marriage is also a religious institution therefore the government should make no laws about it.
Sure, the government is good about the redistribution of wealth and taking from one and giving to another. But while government is good at printing checks, the government cannot effectively address virtue issues ofttimes at the heart and cause of the situation. Thus, government welfare keeps people dependent on the welfare and cannot rehabilitate the dependent citizen leading to self-sufficiency and true freedom.
Only Religion can effectively care for the needy and provide true accountability. Pure religion also is meant to keep its people "unspotted from the world". This accountability the government can never do. Government needs to get out of the business of religion, and religion needs to administer its basic prime directive by carrying the burden of both providing welfare and teaching and expecting virtue. Remember, Christians are not to take the Lords Supper unworthily which provides the basis for divine accountability and expectation.
Socialism is also unconstitutional because the federal government derives its power from the people. Accordingly, the government cannot operate beyond the rights of the people. If it's illegal to walk into your friends house and take something, the federal government shouldn't be able to either. Since the government is a man-made institution, the creature cannot exceed the power of the creator.
Marriage is also the business of religion. Yes, marriage is the greatest civil rights issue of our day. But the civil right that has been violated is the right of children to be raised by both a mother and a father, and soon as advanced fertility technology is being rolled out, to receive a full genetic inheritance from both a man and a woman. This is the only difference between marriage and civil union. Let same-gender couples have all the insurance, employment, tax, medical-decision making benefits. But same-gender couples are not married and should not create offspring together using advanced fertility technology. But even knowing this, the federal government should be unconcerned with this this because marriage is religion and governmemt should make no law with regard to religion. It can only prosecute afterwards for harm.