The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people. - Ninth Amendment
And note - gay marriage and abortion have majority support among the American populace, and in many states where they have currently been outlawed.
Calling for a Constitutional Amendment for this is a red herring, as rights do not have to be enumerated in the Constitution to exist. The Constitution doesn't even support the Supreme Court's right of judicial review.
And guess what -- in states like Alabama, the people of that state have elected politicians that choose to regulate things like abortion in a manner different than what would be the case in a state like California. On the flip side, you have states/municipalities that regulate the second amendment -- something DEFINITELY in the constitution, and not in a "squint really hard and it sorta makes sense" way like abortion -- much more stringently than other states. The system is working as intended.
The issue is that you're expecting every state to have the exact same cultural attitudes towards things like abortion. They don't. The majority of people in certain states are against it, and they have voted accordingly.
You are right that all rights are retained by the people, but what has people mad / worried is the states legislating against the will of the majority (specifically because there is nothing stopping them from doing so at a federal or constitutional level).
[0] https://en.wikipedia.org/wiki/Interracial_marriage_in_the_Un...
[1] https://talkingpointsmemo.com/news/braun-supreme-court-inter...
Stop acting like there's some mainstream Republican movement to ban gay and interracial marriage, it's obviously not true when you have to sensationalize the titles of your own linked articles.
Edit:
And it's not even "they" want it to be left to the states. It's a single individual who even mentioned anything about it, and even they "backpeddled" (i.e clarified what they said after the media twisted their words for sensationalism).
> they want it to be left to the states
and republicans are already changing their platforms to include even stronger anti-gay platforms [1] as has been historically (ill just link to their platform directly) [2]
[1] https://www.houstonpublicmedia.org/articles/news/politics/20...
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[2] https://www.presidency.ucsb.edu/documents/2016-republican-pa...
Traditional marriage and family, based on marriage between one man and one woman, is the foundation for a free society and has for millennia been entrusted with rearing children and instilling cultural values. We condemn the Supreme Court's ruling in United States v. Windsor, which wrongly removed the ability of Congress to define marriage policy in federal law. We also condemn the Supreme Court's lawless ruling in Obergefell v. Hodges, which in the words of the late Justice Antonin Scalia, was a "judicial Putsch" — full of "silly extravagances" — that reduced "the disciplined legal reasoning of John Marshall and Joseph Storey to the mystical aphorisms of a fortune cookie." In Obergefell, five unelected lawyers robbed 320 million Americans of their legitimate constitutional authority to define marriage as the union of one man and one woman.