Are laws set to liberate people or are laws set to restrict people? Are laws set to protect people or are laws set to oppress them?
The whole idea of repealing Section 377A is, in my opinion, about whether this particular law is there to restrict people or to give them freedom. I personally feel that it now oppresses people more that it frees/protects them. So, I would think repealing it makes more societal sense in the country we live in.
It is not, and never should be, about whether homosexuality destroys the institution of marriage, whatever the fuck that is. The 'institution of marriage' is not found in the Bible. It was established by clergymen of different faiths by interpreting religious texts. It is a human creation.
How I know it is a human creation? Because different faiths interpret this 'institution' differently. Jewish and Christian scriptures mentioned on multiple occasions of men having more than one wife. King David, King Solomon, Jacob/Israel, to name a few. Islam allows men to have up to four wives and I genuinely wonder how that came about. So where does it explicitly say "monogamy between one man and one woman is the only God-instituted law"?
While I accept that Jews, Christians, and Muslims all agree homosexuality is a sin, we are not living in a Jewish, Christian, nor Islamic state. So, the call to protect the 'institution of marriage' is really the religious people trying to oppress those who don't believe in God and/or believe that homosexuality is wrong.
To throw in a curve ball, if you want to institute your religious beliefs in marriage, you should accept the whole canon. Where adulterous women must be stoned, where polygamy (specifically "one man, many wives") is allowed, where a widow will become the dead husband's brother's wife, where barren women are frowned upon. Pretty sure these laws would look very ancient to many of you.