That's a great question and one we plan on exploring in posts in the very near future through @steemitblog, so be sure to give that account a follow if you haven't already. In short, SMTs won't take away from Steem because they will actually create more demand for Steem. The reasons why are technical, but I don't think that's the important part. The important thing is that every community has their own values and their own social norms. Different people value different things in different ways. That's why they need their own currency. We've spoken to countless developers and community leaders over the years and they all say the same thing, "We want our own Steem-like token." In order for Steem to be adopted by the masses it has to offer them features that they find valuable. One thing we know for sure: people like creating their own cryptocurrencies. As the team behind the blockchain, it's our job to make sure that everything ties back into Steem making the whole thing economically sustainable and scalable, so that when features are added that do add value, all stakeholders share in the upside. If you would like to learn more technical details you can read the whitepaper at steem.com.