I think you make some good points, but, I’m unclear on the 14th amendment “equal protection” argument.
Everyone is already treated equally under current marriage laws. Any eligible man can marry any eligible woman. We’re all limited to one partner at a time. We all are limited to an opposite sex partner. The fact that a homosexual man doesn’t want to marry a woman doesn’t negate the fact that he has the same right to do so as anyone.
Further, homosexuals are not a protected class under federal civil rights laws. The laws classify us all as men and women. There is nothing about gay men and lesbian females in the federal law, thus, there is no legal basis to say that they are treated unequally somehow in marriage laws. At least there is no legal basis unless a judge decides that homosexuals “should” be a protected class.
We can all make policy arguments for and against same-sex marriage, but, clearly the judges are bending the law to rule for same-sex marriage. If homosexuals were a protected class under civil rights laws, then the argument under the 14th amendment would be much stronger.
To me, the place to make all these arguments is in the legislatures, not the courts.
That is exactly the problem: we have reached the point at which the equal protection argument is tearing up ALL of the limits you mention. Yes, gays have the right to marry the opposite gender, but they don't want to do so. Yet they want the financial and legal benefits of marriage, so they have now successfully argued that the 14th amendment should protect that option on an equal basis of opposite-gender marriages. They have worked around the protected class argument and gone for a straight 14th amendment victory.
So my point is that we have lost this argument and must therefore develop another approach (previously outlined). Your points seem to be exactly what was lost in this California decision. Common (gender) sense and tradition have no rational legal standing any more. Religious practice was ceded once the government and states got involved in licensing marriage. Once this hits SCOTUS (and wins), I expect that the only limits left regarding marriage will be that of 'consenting humans of age'... two or more.