Your brother has given you advice based on his feelings and knowledge of you. He worries that you might be misled by someone here, and he may be right. It's a personal issue, and if you feel uncomfortable, then he may be right, and this might not be the place for you.
I know there are apostates here, and those who seek to pull people away from Jehovah. I have also encountered these people in person, at their own doors. I don't 'count time' here, either, and I try to be very careful about who I talk to here. If I know they are apostate, I don't look at their questions or answers. I don't need their muck filling up my mind. Jehovah rejected them for a reason. They are blocked on my account, if I know them to be apostate. There are some who claim not to have been disfellowshiped from the christian congregation, and I have to take them at their word, until their words prove otherwise. If you met someone face to face who told you they used to study-you wouldn't turn your back on them, and they may be lying, too.
You just have to use your best discernment when on the internet-we are cautioned to be careful, and your brother may see a problem you can't.
In the area I live, it's hard to find people at home, and since our main employer is the prison system, it's a little hard to get to people who work in there. Our congregation does evening witnessing, letter writing, phone calls, business territory-all in an effort to reach people. The world is changing, and to me, this is just one more way to witness.
I can think of several people, just in the couple of years I have been here, who have been activated, or re-activated, partially by the friends on this site. Honestly, If I hadn't seen these beloved ones advance, and give part of the credit to the friends here, I don't think I would keep coming back. This experience here has me torn-on the one hand, I have made friends that I hate the thought of losing touch with-but the nastiness of those who oppose us is so much more overt than what I encounter in face to face ministry. For now, personally, I will stay, and if I should ever lose my joy here, I will leave.
Several elders in my hall know I answer on this site, and one actually helps me with ancient languages, and original meanings, since greek is his hobby.
It's important to have balance, and not 'use the world to the full'. You should listen to your conscience, and give weight to what your brother has said. If you live at home, and your parents are witnesses, too, you might want to ask their opinion.