Don't go combat arms.
Go for a trade that can get you some civilian applicable skills for when you inevitably get out. Even if you are a true believer, military tend to retire a little earlier than their civilian counterparts. It's only 20 years of service to get full bennies. It's better to get some useful experience on the job than rely on the GI bill to go to school for something you could have been doing as your actual job description already.
If you want to join to help your fellow man, you'll probably have a better time in something technical or administrative than in combat arms. It's less glamorous to be a FILTHY POG but a typical work day in garrison is stupidly pointless as it is. But if you're doing paperwork or testing radios or resetting passwords, it's at least more useful to your mates than cleaning a pile of weapons that haven't even been fired recently. When you do go on operation/deployment you'll be doing things that have a tangible effect on operations and might even be wholesome in their own right -- digging wells in africa or fixing telephone lines after ice storms or whatever. Even if you don't support the operations you end up on, at least you can look at the more routine work you're doing and be like "well at least I'm helping my coworkers have an easier go of it". I can't imagine it's so easy to find being in the infantry as fulfilling from that standpoint.
Like others are saying, you're just gonna be disappointed if you go in expecting to be a hero of western values and so on. It's just a job, and the day-to-day is actually kinda boring. And if you want to protect your fellow man and avoid jewry, you should go become a cop or firefighter or something, not a soldier.
