Why make such blanket statements and logically loose arguments? You might as well advise the commenter to refrain from buying knives and baseball bats, too. Because, statistically, you're
much more likely to be killed with a knife or a baseball bat in the commission of a crime.
A gun is a tool with a high(er) degree of lethality. Just like any other tool in the house, if one is not trained and practiced in its use, one is far more likely to make an error when using it in an emergency situation.
If you want to make blanket advice statements, at least qualify them. The responsible thing to say, in this situation, is, "Please don't buy a gun without undergoing proper training." Guns are a force multiplier/equalizer and we live in a society where guns are easily obtained by criminals. Telling law abiding citizens to strictly avoid force-multipliers like firearms, in our society, benefits the criminals and anti-gun lobby -- but it doesn't benefit the person to whom you've replied.
In fact, you've only perpetuated the cycle of fear by trying to instill more fear in your argument to avoid guns (lest they kill a family member, murder an innocent person or be shot with the firearm).