I can't speak for everyone, obviously. But I can honestly tell you why I'm so against the current government making *any* laws about the 2nd Amendment. And the answer is, in complete seriousness, the way they handled gay marriage.
As we both ask and acknowledge every time we say the pledge of allegiance or sing (the full version of) the national anthem or sing "God Bless America," God has blessed this country tremendously. But yet despite all of His blessings (not to mention the plain fact that He is God, and we are not), we spit in his face and overtly rejected His authority when it came to gay marriage, and even more so when we began to actually CELEBRATE something that is so clearly an affront to God.
Now, this country allows a lot of sins, including greed, sex out of wedlock, and so forth. You can't legislate someone's heart into loving God (which requires obedience, John 14:15-24), nor should we really try. But it's a different issue entirely when we try to re-define something that God has already defined. At that point, we are no longer simply rejecting His clear commands and authority, but actually saying that we know better than He does. God defined marriage as being between man and woman, and for the purposes of producing godly offspring. (Malachi 2:13-15; Matthew 19:4-6)
We do not have the authority to take His place on the throne, or to change His commands -- but yet, the world has always tried to do those very things. The first time insurrection against our Creator got out of hand, He destroyed the world for rebelling against Him. After doing so, He provided the rainbow as a reminder of a promise that He would never again destroy the world by flood. (Genesis 9:13.) The next time that a large group of humanity got dangerously out of hand was Sodom and Gomorrah. God destroyed those places largely for rampant sexual immorality and extreme homosexual behavior, as well for generally rejecting Him. But yet we take those very things, combine them, celebrate them, and then use God's rainbow to indicate our "gay pride." (And even leaving all of that aside, don't forget that pride itself is an abomination to God (Proverbs 16:5; see also, e.g., 1 John 2:16).)
When we do those things, we spit in the face of a God who has blessed us so tremendously, time and again.
All of that was bad enough. But then the government took those things, and then began to force even God's own people (the Christians) to either participate, or else be subjected to financial punishments or even incarceration. Now they're trying to un-accredit Christian universities and force various Catholic institutions to participate in their godless ways, including paying for abortions and birth control and forcing them to hire people who are living in open sin. (I'm not defending the Catholic church per se, but I am defending their right to function as an entity separate from state control.) What's next -- forcing Christian churches to hire atheist pastors? Forcing Christians to remain silent about the portions of the bible that society deems to be "offensive" or "hate speech"? We are headed down an extremely slippery slope, careening towards a very dangerous ending in the ways of God, even if not in the ways of the world.
And how did we get there? Here's how this all plays into my concerns about touching the 2nd Amendment. When the whole "gay marriage" "debate" started 10 or so years ago, or even just going back five years ago, the constant refrain from the left was, "Just let the gays get married. It won't bother anyone else." First, you see how quickly the swell of public opinion changed. Fifteen years ago, gay marriage was an absurd idea to all but a relative few. Today, to even question the idea of gay marriage results in you almost automatically being accused of hatred, bigotry, and homophobia. And I know, because I've been personally accused of ALL of those things.
But more to the point, once the LGBT community / lobby got an ounce of power (and the wave of public opinion) behind them, suddenly "Just let us get married, we won't bother anyone else" became "We're going to force the Christians to participate in our wicked ways, or else!"
You see, to most non-Christians, bondage and oppression come in the form of physical slavery, of being forced to do things against your own will. But to most genuine Christians, the worst form of bondage is bondage to sin. God has changed our hearts from the inside to the point that we GENUINELY hate sin and GENUINELY love and want to obey God's ways (see Ezekiel 36:27 -- if you read none of the other verses that I posted, please read that one, as it's essentially foreshadowing the NT Gospel via an OT prophet). To tell us that we can't obey God, I would seriously sooner sit in jail (or honestly even be killed) than to be forced by the government to sin against God.
To us, government overreach in telling us how to worship God is the worst form of tyranny there is -- and I mean that from the depths of my soul, and from the bottom of my heart. I'm not just saying that to make a point for a debate. I sincerely mean those things, and so do A LOT of other Christians.
And so what's the Constitutional answer to government tyranny? The 2nd Amendment. (Along with obedience, preaching and prayer, which are the spiritual answers.) Most Christians have no desire to ever shoot someone even in self-defense, let alone to go and shoot up a school or nightclub. But the mere ability to bear arms is designed to protect us, first and foremost, from governmental tyranny. Simply owning guns makes it harder for the government to just impose its will and overstep its bounds, because they know that the citizenry is capable of fighting back if need be. And that right there is why this administration in particular has zero chance of making any changes on 2nd Amendment issues, and it's precisely because of how much they overstepped their bounds and rammed homosexuality (and now transgender stuff) down our throats.
"For I did not shrink from declaring to you the whole counsel of God." (Acts 20:27)