Abandoning our practices and culture would be seen as a victory for terrorists. There's a huge effort ongoing in Pakistan to limit Shia processions on the streets and the threat of terror is their main talking point. We simply can't give up because it will mean that the terrorists and our enemies succeeded, or in other words we lost or they were able to scare us. That's unacceptable for us.
The religious aspect, from our point of view, is that our processions are remembrance of the atrocities that were perpetrated against the Prophet's family, certainly they expose certain characters who were involved in these, directly or indirectly. They either don't like us to remember history or deny our interpretation of it as it challenges their beliefs and interpretations, so some of them resort to violence to stop us.
Another important factor is the remembrance of the massacre that was perpetrated against Iman Hussain(AS) and his family is at the heart of Shia culture. If we get scared of martyrdom then what's the point, our whole existence would become hypocritical.
I could go on but if you are interested, then google about Shia history.
Thanks for your interest, it's a very good question that some people don't appreciate the answer of.