2) In sex-based equal protection challenges, intermediate scrutiny applies. In such a challenge, it must be shown that the law or policy being challenged furthers an important government interest in a way that is substantially related to that interest
3) The 14th amendment applies to the states, so the 10th amendment is not a shield here. "... nor deny to any person within its jurisdiction the equal protection of the laws."
4) The Supreme Court dismissed Virginia's argument that "anyone can marry the same race, therefore there is no racial discrimination." This logic easily applies to the notion that "anyone can marry the opposite gender, therefore there is no gender discrimination."
So tell me the important state interest served by same-sex marriage bans. Since you're the legal and constitutional expert here. Surely, as a believer in small government, you must agree that for the government to place a restriction on its citizens, it has to show a good reason. Otherwise it has no business making that decision for us. Right? Because that's what I believe.
Failing that, feel free to point out errors in my legal thinking.