Dont u allow tor on your normal URL ? How did u get that .onion address ? Is there anything illegal associated to it ? Is there any vulnerability like XSS attack etc for having a .onion address ?
Normal URL allows TOR, but if you use TOR, it will be safer if you access the site through .onion address:
http://www.btcfeed.net/news/rogue-tor-node-hijacked-blockchain-info-accounts/.
Using TOR doesn't mean you are doing something illegal, it is just a technology that protect your privacy. Regarding vulnerability, it is just like having multiple domain for the same site.