It is alright to explain something to a friend to be clear and avoid misunderstandings, however when someone is manipulating by asking "why" we are not obligated to answer the challenge.
When a child asks why you will not do something or why you will not let them do something it is a ploy to wear you down to eventually get what they want. Adults do this too from time to time, they want to know why you will not do something so they can argue why it's not a good reason.
When we have boundaries according to God's Word we need not explain to anyone "why" we have that boundary or why we "choose" to have that boundary. Even if we have reasons that are merely our own choices it is alright to keep those boundaries. No one is justified in judging our personal choices.
It is not godly to allow others to dictate our course, they cannot have the knowledge of what God wants for us or our inner spiritual needs.
Often our culture pressures us to do what they do and be like them and even offended if we choose another way. There have been many times I was judged for not doing something others wanted me to do. I felt the pressure of others to do what they wanted but at the same time had a check in my Spirit that it was not God's will for me.
It was a relief and joy when God showed me that I do not have to do what others want unless Christ in me was telling me the same things they were asking.
Psalm 143:10
"Teach me to do Your will,
For You are my God;
Let Your good Spirit lead me on level ground."
Galatians 5:18
"But if you are led by the Spirit, you are not under the Law."
Acts 15:28
“For it seemed good to the Holy Spirit and to us to lay upon you no greater burden than these essentials:"
The ideas others have of what we should do have no value unless the Holy Spirit is the One telling us the same thing. If our friend comes to confirm what God has already told us, then their idea is from the Holy Spirit and is confirmation of what God has said to us.
There is such freedom in Christ that we are not under the control of anyone other than the Holy Spirit. The cultural mandates that press in on us continually will have no influence on us.
We do not feel the pressure when we are free to say no. The culture's responses to our boundaries have no effect when we are free in the Lord from their pressures. Any negative response from the culture for not going with them bounces off as if like a feather hitting us, we feel nothing at all.
May the Lord give us compassion for the needs of others but discernment to know when something is merely a desire and not a need.
When we drop the pressure from the culture to be seen as a good person according to their idea of good, we can move freely in the power of the Holy Spirit without guilt.
We are not led by the culture, but by the Holy Spirit.
Romans 8:14
"For all who are being led by the Spirit of God, these are sons of God."