I went to a country church a few Sundays ago. There was a fine elderly gentleman who greeted with me and sat beside me all through the divine service. After the service, they had fellowship over coffee/tea. We got to chat at length and I got the chance to speak to him of my journey. This fine Christian man, now retired used to work for a prominent publishing company. He said he took care of the religious publishing division of the company and he got to read a lot of theological stuff. If I am not mistaken, he even explored for a time, other denominations outside the Lutheran Confessions too. So after hearing of my journey, he asked me with much concern - "do you not consider Lutherans weak on sanctification"? I said, "yes, I do, and I am perplexed by it because you would think that the one strong on justification would have been strong on sanctification too". It seemed my gentleman host has been bothered by this too and did not know what to do with it. See another one bothered about this too.
Over the years, I have heard Lutherans in the Internet proudly said of themselves - weak on sanctification. Mind you they do not say this with shame, they even boast about it. Like one time, I heard a pastor said that when he is amongst some Baptists - the more he would drink beer in front of them, so he could show them how free he is. I suppose the man wants to purposely offend.
1 Cor 10:9 But beware lest somehow this liberty of yours become a stumbling block to those who are weak. 1
It is one thing to admit one is weak on sanctification but sad about it, versus saying one is weak on sanctification and boast about it too. I would say the first one is coming from a repentant heart, the second one I suspect is coming from an anti-nomian bent (either consciously or unconsciously).