"and all your family was killed" IMO we dont need so extreme examples. it is too bad :) "too is always negative" it can be used to mean "also", for instance, "I like pizza too" but even when it is to indicate an excessive degree of something, it can be positive, if I say "This cake is too delicious" it means I guess that the cake is extremely delicious and exceeds expectations -> what is good

This is not a common use of "too" but it is acceptable. When you say "I am too happy" it is likely to be interpreted as "I am too happy for it to be possible for me to express it in words". Normally, "too" expresses an undesired excess, but it is OK to use it this way because an undesired excess of happiness is simply not possible. There is no possibility of misinterpretation.