If you are of the view that ideas are worthless and execution is all that matters, then there is no innovation anymore. Facebook can out-execute pretty much any small startup if they really wanted to go into a space.
The only advantage Facebook has in entering an entirely new space is capital, which is not a unique advantage. The unique advantage they have of modifying their social media platform, is that they have by far the largest platform, and if the only differentiation of the smaller competitor can be easily replicated, it will be quite easy for Facebook to compete, without even deploying much capital. Thus, if someone wants to compete with Facebook, there has to be either significant IP, or a feature that isn't as easily compatible with Facebook's platform (note that Facebook also tried to replicate Snapchat early on, but that failed). I am not saying that ideas are worthless, but many are not easily defensible as a business strategy, and I don't see the reason to blame Facebook for leveraging their unique advantage by adding compatible features that have been validated by other companies, nor for deploying their capital to acquire such companies. One could have plenty of ideas for how to leverage a large social media platform, but without access to that platform, and especially if a competing much larger platform can easily replicate such ideas to drive you out of business, there would not be a strong case to make for these ideas being true innovation in the context of business.
Back in my day, Microsoft entering your market was taken as a validation of the market and confirmation that you're on the right track. Being a small player meant you could be more agile than the lumbering giant.
Being small also means you don't have the same opportunity costs on financial investment - where Microsoft could get a better IRR for that investment money, being small means this is the best return you can get.
I suppose you could have said similar things about Microsoft in the mid-90s when they would vapor-launch a product to wipe out a threat or soften up a buyout.
The bigger issue is that they bring in startups, have them tell them everything, and then decide not to buy the company. There are many stories floating around about this and it is highly unethical.
I don't know Facebook's policy, but many companies employ 3rd party consultants to do due diligence. The IP is not communicated to the suitor until after the purchase is complete, only an assessment of the quality of the execution. I learned this process first-hand.
