I hate it when people call the frequency 121.5 MHz "guard".
"Guard" is a programmable channel in military radios and can be any number of frequencies. This frequency is not necessarily 121.5 MHz.
My two cents worth is brief traffic on this frequency here and there is not too much of a problem. It's been happening for years and will happen for a long time to come.
Don't blame it all on QF et al as most of the trafic I have heard on 121.5 has been military. Rather than baging the industry for monitoring a frequency for the good of all, how about thanking the industry for doing so, and accept that that the result of this monitoring might mean that ppl call each other on it from time to time.
If ppl stop monitoring 121.5 MHz in favor of listening to 123.45 MHz then you have made a decrease in the functionality of 121.5 MHz as a well monitored emergency channel which would be far worse than any purist idea of keeping the channel clear!!!
GGAL