In one of Mike Winger videos on divorce, he answers the objection that if adultery is grounds for divorce, this encourages adultery in order to justify divorce. There are two main problems with this objection (along with his very good answer).
The first is that even if this was the case, the objection is actually an attempt to answer scripture with philosophy. At the end of the day, regardless of what you think the implications of scripture are, it says what it says, and more importantly, it comes from who it comes from. That is, it comes from God. As scripture comes from God, we have no right to edit it, or attempt to "correct" it. We don't get to add to it, we don't get to take from it, we don't get to "make it better", or elevate our traditions to its level. Our only right as human beings is to study and obey it. So, no objection to scripture can be valid, and scripture does teach that, in the case of adultery, divorce is 100% valid.
But beyond that, the objection doesn't work because it betrays the heart of Christianity. See, as Christians, our hearts ought to be reformed. Our sinful natures need to die, and we be raised to life in Christ. What that means is we shouldn't be testing our limits, and when we do, that tells us a lot about what we really think of Christ. If you are so depraved that you would commit adultery, which the Bible very clearly defines as sin, just to get a divorce, you might as well just get the divorce. If you don't care that the Bible opposes adultery, why even pretend you care that the Bible opposes divorce?
With the Lord, it really is all or nothing. Sure, we're all sinners, and He advocates for us when we fail, but if you look at that as an excuse to sin, rather than a motivation to obey, you are probably not a Christian. Salvation is a safety net, not a hammock.
Of course, this goes beyond just divorce and adultery. There are many sins we can justify if we are reckless enough. Heck, we can justify all sin if we try. I remember when I was new in my faith, having just found out homosexuality is not permitted in Christianity. But God will forgive me, right? So I shall sin, that grace may abound! Praise God, He won that fight. It was utter folly, I should have never tried to abuse His grace like that. If I am truly saved, why am I treating God as a get out of jail free card? If you are truly saved, why are you? Obey, or cease to pretend you care. If you're saved, act saved and obey. If you're not saved, admit you're not saved, repent, get saved, then obey. Let's have no more of this recklessness.