in short....accepting a strangers friend request isnt going to "pierce" your computer firewall and steal your data BUT....depending on your level of preperation it allows said person to get more information about yourself than you are willing to give. Maybe your privacy settings offer more info than your public ones? Your country of residence, your gender, your real life name etc. These kind of things.
On steam a lot of traders are using the friend request to initiate trading offers or requests and this is probably an automated system without any conscious oversight.
I would advice to question your personal benefit from accepting it. Do you know this person? Do you have anything in common with him/her? WHY does this person wants to be your friend? You can as well shoot him/her a chat message to figure out what to do.
Personally I ve been burned a couple times on steam by so-called "friends". One was doxxing me, the other was sending me a virus link disgused as some funny video. I m not interested in having a large number of friends. I understand that some people find pride in this (hey man, I have like 5000 friends....how about you?) you just gotta figure out what you want.
If you want friends accepting blind requests wont help you with that. And if you are going to accept steam friend requests to support your activity there (multiplayer or trading) just make sure your personal bio is in order and doesnt allow too much insight into your private life.