Sheikh Salman al-Oadah
We do not see any problem with Muslims joining with others in such gathering to share positive ideas, promote justice, and express their condemnation of injustice.
Allah says : “Allah forbids you not, with regard to those who fight you not for (your) faith nor drive you out of your homes, from dealing kindly and justly with them: for Allah loves those who are just”. This is in fact the Islamic manner which we have to follow and it is at the same time a good way of calling others to our religion.
You should avoid all un-Islamic or undignified behavior. Muslims should always maintain their Islamic modesty and moral integrity.
May Allah guide us always on the Right Path.
Source: Islam Today