... Ophelia's death was an accident. She did not mean to die. She simply had no idea of her danger. It's no different than if an infant fell into the river and didn't understand that it would drown if it didn't try to get out.

But obviously Shakespeare wants the taint of suicide on her death.

The taint does a few things:

First, it allows both Gertrude and Claudius a chance to show that they thought very highly of Ophelia. They would not have insisted on a Christian burial and attended it themselves if they had not felt it was something that they owed her and felt she deserved.

Second, it makes Laertes even more angry with Hamlet. If Hamlet hadn't killed Polonius and then left Ophelia completely alone, she wouldn't have gone mad and drown. That's not exactly sensible reasoning, but that's how Laertes sees it.

Third, it gives Laertes his best line in the play, IMHO: "I tell thee, churlish priest/ A ministering angel will my sister be/When thou liest howling." I love his ability to feel the right way about all Ophelia's death, even though he hasn't always been the best sort of brother.