What do you think “both siding” entails?
It is the simple reduction of two completely disproportionate responses to the phrase “both sides do it”.
The same logic keeps being applied to Russia’s invasion of Ukraine. Both sides are fighting, they say, so both sides share equal responsibility for the destruction and for making peace.
I believe you when you say it isn’t your intent to do so, but in that case you are doing so obliviously. You don’t even know who the commenter is, so it’s pure assumption on your part that they’re even left wing to begin with.
In that case you are naively both-siding this issue.
To help clarify: if somebody was to read your first comment, are they likely to infer that the two sides are equivalent?