Some SEO bloggers and other industry observers are adamant that buying likes is always a bad tactic to use. Some others are extremely enthusiastic about the practice (and are probably the ones trying to sell you the likes). The real answer is somewhere in the middle - it depends on your business's situation, where you're at in your current stage of growth, and where you want to go. But everybody is entitled to their opinion and might have some valid points.
Why are there detractors?
Many social media bloggers (in public at least) absolutely despise the idea of buying likes. This might partially be because they genuinely disagree with its effectiveness, are concerned about its effects on your EdgeRank score, or because they're actually a bit scared about the ease where others can catch up to their prodigious and inflated follower counts.
You can look back to the history of Twitter and see how in the early days a lot of people spent massive amounts of time following and unfollowing everybody under the sun to try and grow their Twitter count as fast as possible to gain social proof. Because Twitter's API allowed automated tools that follow and unfollow people in massive bunches to quickly emerge, many of these types of tools were used by forward-thinking bloggers to get in on the ground floor, so to speak, and initially hit some level of influence by inflating their follower count. Now the question is, if many of these same people recognized the influence that they gained just by virtue of the fact that they have a big follower count where others do not, why would they claim that getting more Facebook likes is worthless? People use these numbers as a sort of filtering mechanism to figure out what pages might be worth their time, or just worthless.
Startups can benefit
Getting more likes on your Facebook page or more followers on your Twitter account or more YouTube views can have a substantial benefit to conversion rates. Unless they've already been funded, most startups don't end up appearing in TechCrunch or Mashable right away. It turns out that a small development team can ask their friends and family to like a Facebook page and most people won't go out of their way to do this (some friends!). So most startups are left pitching the tech media at a disadvantage. They need some media coverage to get traction and likes, but they can't get the media coverage without the traction or money. And they don't have the cash to do massive amounts of traditional saturation advertising. So in this kind of case, buying likes can get you onboard the Facebook train and get you a respectable looking page where you can comfortably pitch bloggers and they'll at least think you're viable enough to interview.
Small Businesses can gain an edge
Buying likes can also be a viable way for a small business to gain the edge. When your competitors all have a few dozen likes, a small marketing campaign that gets you a few thousand extra likes can help you appear larger and more influential than them.
Of course, when you already have a great deal of likes on Facebook, in the hundreds of thousands or millions range, it makes a bit less sense to focus on this. A large and nationally known brand such as Pepsi or Burger King already has a ton of social followers and spending time and effort buying more leads to a minimal gain. In this situation, you should be focusing more on engagement and conversion than outright growth.
Analytics and Testing Are the Key
Regardless of what you decide to do, you should be monitoring all of the types of advertising you're doing. Some businesses in some product categories do very well with social media, and other businesses need to focus more on traditional B2B or B2C outreach methods. But you won't know for certain what works best for you without actually testing things out, and measuring the return on investment. Use any and all analytics tools that you have at your disposal to figure out what works best for you. Set aside a small budget to test out new marketing methods and see if you can find something that gives you a better conversion rate. If you're doing your job and keeping track of this data in a database or spreadsheet, you'll quickly be able to figure out ways to advertise in a more cost-effective manner.