I've read the loved ones of the person who suicided become angry at that person, which is something I find hard to understand. I'm assuming it's because they are sad/upset that the person suicided, hence angry at the person for causing the sadness/grief. If I am correct, it seems like quite a selfish reaction to me.
I don't think anger is uncommon, for the reasons you stated. Not sure they'd show that at the funeral as such though. I think people often try to save face at a funeral.
I think there can be all sorts of blame being hurled around after a suicide. Including blame/ suspicion and shame of those closest to the deceased. Did no one actually notice they were that unhappy? So- to act angry towards them at that stage could come across callous to friends and family. I imagine that they would be more likely to be receptive to the sympathy they are (deservedly) being shown.
Asides though, I think funerals are usually incredibly emotional. I imagine most will be feeling intense grief and loss at that point.
Anger is certainly sometimes present though. Sometimes it's deflected though. I think the most intense hate and campaigning this forum gets is from those who have lost loved ones to suicide. Sometimes I expect it's too painful to hate the person that made the decision to die but also as a consequence, to leave them. So, they blame it on something like mental illness- that person wouldn't have done that to them if they were thinking logically. Even their (inaccurate in my opinion) perception that a forum like this encouraged them to do it. Plus, they hate anything that enabled their loved one to do it. The internet, this forum, the person that sold them the equipment, the government for not having stricter regulations. Of course, there will be examples where there is a perpetraitor- a bully or abuser.
I find it really sad too that people get angry. I think it's disappointment/ disapproval too- as in: 'Why didn't you fight harder (for me.)' I also think that being made to feel guilty about something (they may actually feel like they hadn't done enough to support the person) does sometimes make us feel angry. Who likes to be made to feel like they're a bad person who didn't do enough to help?
I think it's just a whole bunch of unpleasant feelings they don't want to have that they wouldn't have if the person were still alive. I wonder if they really consider though that- if that person were still here- what's the likelihood they would be ok? Kind of weird isn't it? I want you alive and suffering for my sake. I think we can feel angry at them for that but maybe it doesn't tend to reach the same level. Or, people CTB before it does maybe.