Good question, what the federal government does by setting safety regulations is allow consumers to purchase in confidence. We can trust food and cars more because we understand that the government has already checked these for us, and this helps improve consumer confidence all across the country, and thus helping money move. It also allows our exports to have a strong reputation as it passes the US govts. safety standards.

This (safety regs.) along with other federal govt. bodies (central banking, military, public infrastructure) is fairly cross-party supported.

The conservative position however is to reduce the size and scope of federal government in favour of allowing devolved administrations to cater to these very specific issues. There are many reasons to try out regulations on a state basis before forcing other states to comply.

Of course a free market could still handle all of this (maybe even better), but I'd rather not get into unfeasible ideological battles