Trojaned installers by download.com were rampant back in the day. They would take your program and wrap it up in a nice little installer wizard and then also stuff a bunch of adware and spyware in there with it
Anyone not technical enough to compile a binary has to give up trying to use it or risk some unnoficially distributed executable .
Not to mention that the md5 checksum is a very poor choice for this purpose because of the ease of creating md5 collisions.
That's the whole point of using a cryptographic signature backed by a web of trust instead of a mere hash.