"But That's the Old Testament!"

When critics/skeptics point out issues in the Bible, a "response" they get pretty often is "but that's the old testament!"

And it is not usually followed by any elucidation, at least in my experience. You're just expect to accept that your criticism is now somehow "invalid" because of this statement they've just uttered.
And I'll admit, I said this too when I was a Christian, much to my current embarrassment.
I guess it's a way to shut critics up, especially since most criticism of the Bible comes from the old testament.
So I'll be unpacking this very odd statement and the intention(s) behind it.

The first and obvious question to ask is, what does it even mean? If the problematic verse in question is from the old testament ... so?
Well, I'll try and explain the Christian reasoning behind this response.

The idea is that Jesus's death and resurrection sort of "annulled" the old testament, or more specifically, the law.
With Jesus's coming, came grace and salvation, so people do not have to live by the law, they do not even have to regard the law, they just have to believe and be saved... This is supported by some passages like Galatians 5:18, Romans 7:6, and Hebrews 8:13 which speaks about the old covenant (or testament) being replaced by a new one, making the old one irrelevant/obsolete.

It may seem like this makes the situation better, but it actually makes it worse. Because why would an all-knowing, unchangeable god need to create a new covenant to replace the old one? Didn't he know from the beginning that the old covenant wasn't going to be viable? And if he did, why did he go ahead with it?
Furthermore, the decision to do away with the initial covenant and create a new one implies a change of mind, which isn't supposed to happen.

Also, isn't the old testament also god's word, inspired by god himself?
The Bible says that all scripture is god-breathed and useful; doesn't "all scripture" include the old testament? So why is it irrelevant? How could it be irrelevant? How could any part of god's word be irrelevant or obsolete? Doesn't this go against the belief that god and his word is perfect, unchanging and timeless?
In Hebrews 8:7, the writer says "For if that first covenant had been faultless, there would have been no need to look for a second one", admitting that the original covenant was flawed, but how could it? How could god's covenant be flawed when the law of the Lord is perfect (the old covenant includes the law)? 

Even god admits that his original covenant was not good enough.
So the law of the Lord isn't perfect, contradicting Psalms 19:7

This also raises another question, does god's morals change? One of the main points of the moral argument is that god's moral are objective and timeless which gives us a perfect moral standard.
But when you bring up the morality of many of god's acts in the old testament, another reply you hear often – in addition to "it's the old testament" – is "it was okay in those days" or something along those lines. This implies that god's morals are changing along with that of humans. Most Christians would deny this, but indeed, when you say that killing an entire tribe of people (including the babies) was okay in the old testament times, but not anymore, you're saying that god's morals have evolved along with humans'.
If not, would it still be okay for us to march into a community and kill them all for the cause of god?
I don't think any Christian would say yes to this.

It's also very telling when you bring up an issue or problem from the Old Testament and instead of being presented with good arguments or explanations, you're simply told "but that's the old testament!"
It gives the impression that the old testament is something the believer would rather not deal with. Almost like they're trying to avoid the topic or downplay the problem because otherwise they don't have any explanations or justification for god's apparently wicked acts.
So they pretend that because it's the "old" testament, god is allowed to be a dick.
Funnily enough, Christians regularly preach about the Ten commandments, tithing and other things only found in the old testament. Yet when we point to disturbing passages in the same old testament they try to invalidate our point by saying "it's the old testament".
So, the old testament is relevant and true when they see a passage they like in it, but irrelevant and obsolete when we point out problems.

Many Christians are embarrassed by the old testament, and for good reason. Their god isn't portrayed in a good light; many, if not most passages of the old testament, depict god as a something of a maniacal, cruel tyrant. Not very loving or kind. But if this is a good, perfect, all-knowing, all-powerful god, that perfectly loving nature should be seen in all his works and manifestations, not just in the "new" testament.
So if he appears cruel, unjust, unloving, malevolent, etc in any of his works, even if it's the old testament, then it's still a problem.
Reminding skeptics that "it's the old testament" doesn't take away the problem, it only complicates it.

Also, Happy New Year!