OR gate vs. connecting two wires?
What you have to understand is how logic level H and L are represented.
Both logic levels H and L are represented by two voltages, i.e. L does NOT mean floating potential or "not connected".

L means the voltage is (close to) 0V, i.e. connection to GND. 

And of course H is indicated by a higher voltage, e.g. 5V, i.e. connection to positive supply voltage.

So if two digital outputs have different values (H and L) connecting them would cause a short circuit, not an OR gate.

In very most cases in digital logic connecting two outputs together is wrong.

Exceptions are 


so-called tri-state outputs which can be in a third state "Z". Z actually means high impedance, i.e. "no connection" and  
so-called open collector (or open drain) outputs which can be AND-wired (similar to what you wanted to do for OR). But then you need an additional  pull-up resistor.