Only 21 Million Bitcoins to ever be Mined... Oh really?

All around the internet there is mention of only 21 Million Bitcoins to ever be mined. This sounds great to many people as it seems to insure that Bitcoins will remain scarce and therefore, will retain value so long as there is demand. Being the curious person that I am, and wanting to know if Bitcoin really is a good medium to long term investment, I began to look into these abundant claims.

Apparently, as I've come to find out, it is entirely possible, in a technical sense, for the developers to increase the amount of Bitcoins to be mined. It seems to be the case that the number of Bitcoins to be mined can be changed. This led me to further questions. What's to stop the developers from increasing the amount of Bitcoins to be mined?

From what I can tell so far, there seems to be huge deterrents to the increasing of the amount of Bitcoins to be mined. It seems that if the amount to be mined was increased, it would be disadvantageous to miners, developers and holders of Bitcoin, which should deter the original amount from being changed.

Some of the reasons that seem convincing are that changing the amount to be mined would take a whole lot of consensus and that, in doing so, it would undermine the value of Bitcoin. This seems to make sense to me but I can't help but wonder if it's really that safe of an assurance. As I am looking to learn more in consideration of actually getting myself some Bitcoin, I am curious as to others' thoughts on this matter.

Can the amount of Bitcoin to be mined be reasonably increased? How could this be done? What are the real limitations to keep the amount the same? What would be the consequences from changing the amount and who would have such an incentive to do such a thing? What would there incentive be? I'm truly appreciative of any and all constructive feedback so please do leave your thoughts on this matter in the comments below!

Thanks for your time and insight.

Sincerely yours,
Wes Minister