Whilst I agree with Brad that it's easy (and wrong) to equate urbex with terrorism I don't share his view that urban explorers have an unqualified 'right' to go where-ever they like.
What often seems to be missed off from such assertions is that incursive exploration has consequences for others, and can affect public safety. I wrote a blog post about this a while back, urging both 'sides' to get a more realistic view of each other. There
is harmless and harmful urbex, just as there is proportionate and disproportionate access control...