You should absolutely send the deck over via email before a meeting. You've already outlined the reasons you should, let's take a look at addressing the cons:
Investors may forward deck to your competitors.
Your deck probably won’t end up in the hands of the competition, but you should assume it will. Don't worry about this too much. Focus on executing your idea so you can make it public instead of focusing on how to keep it private.
Without presenting the deck in person, your impact may be diminished.
Have two versions of your deck. The one you send via email should be short and to the point. The one you present in person can have more details. Take a look at the deck Buffer used for their seed round.
Since people's attention spans are far shorter if they're reading something, you need to craft your message just right. Not only should you make an impact from your "short deck", it should be a demonstration of how good you are at selling.
From Nivi at AngelList:
Write “Proprietary and Confidential. Please do not distribute. Prepared for Blue Shirt Capital,” on the cover of your deck (some companies write it on every page). Investors are less likely to forward it if their name is on it.
Meeting with an investor who has no interest in your product, market or type of business, is going to be frustrating at best. Which is why, without a very warm introduction, you're not likely to get a meeting without sending a pitch deck in advance. Obviously, feedback and referrals can still come out of an investor that says "not interested", but that's rarely a reason to meet.
No reputable investor is going to send your deck to your competition. Investors live and die by their reputation - getting caught doing this once, would be lethal.
Your teaser deck isn't supposed to create impact, it's supposed to create curiosity. Make the recipient curious and you'll get your opportunity to make an impact.
For founders that have concerns about privacy for their decks, DocSend has been a great help in letting them see where their pitch decks end up and if investors have been circulating them internally (for input and interest gathering) or externally. It's a great tool for fundraising especially when you have multiple copies of your deck floating around in the ether.
Happy to provide a special code to anyone who wants to bypass the line and grab an account!
Disclaimer: I work at DocSend