My view for what it's worth.
Burglar deterrent - dog needs to be loud. Doesn't matter about being big. Yappy not so good. My springer is soft, looks soft, but sounds ferocious whenever anyone knocks the door, and would really scare most burglars off. I always tell people that a loud dog is the best burglar deterrent you can get.
But you want one for walking the streets. Hmm. Is it really, really that bad by you? It's not a good reason to get a dog - dogs require time, effort, discipline, love - that's a LOT of work needed if you really only want to scare away undesirables, and the end result is likely to be you and the dog regretting your choice.
If that's the ONLY reason, then I wouldn't advise a dog.
If however, the main thing is you want a dog, and were willing to put all the work in that goes with it regardless... Then yes, the benefit of a (even a friendly, sociable) GSD is that it would make you less of a target for that <1% of people that MAY decide to target you at that precise moment. Robbers pick targets of opportunity.
But please, please, please - if that's the main reason... Don't do it. Spend the money on a monthly membership to the gym, go daily, pump iron and get ripped. It'll be less work for you in the long run.