Likes and other "simple clicking activities" get timid people involved and interacting with others at a base level without risk of trolling and flame wars. This opens them to further more complex interactions. This has been proven time and time again over decades of practice. I learned this from the U/X team at AOL when I managed the Groups@AOL development. Everywhere you went on AOL you could click on a heart or a star rating or something similar. It is also a big part of what made Facebook viral. Many "ordinary" folks are terrified to interact on a new system and with new people. This is a way of easing them into it.