Word of advice, if you really want people to give their opinion, you'd want them to open the post first which usually won't happen with titles like this. The last sentence in your post could have been the title "With Bailly fit should we have started him at CB instead of Rojo?" or something similar.

Now to answer your question, saying Rojo is a liability is harsh. Yes, yesterday's tackle was idiotic and so was the one he pulled off against Everton but two reckless tackles (which he luckily got away with) shouldn't label him a liability.

As Mourinho said, Rojo is probably playing the best football of his career right now and I'm sure Mourinho knows how to deal with him and help him fix those mistakes.