Attachment (aka craving or greed) is one of the Three Poisons. Why is attachment to Buddha not a poison? Perhaps it's related to the Tibetan Buddhist lojong "Don't make gods into demons"?
Attachment to Buddhism and to Buddhist philosophy is a very serious problem, which every practitioner should be careful about, since it's so seductive: it's easy to be perceived as progress, whereas it's the very opposite of progress.
To counter this hazard, some Zen schools recommend that "if you come across the Buddha on the road, kill him!" (Not to be taken too literally.)
My understanding is that the Buddha taught that we should not attach ourselves to him or his teachings. If we find that his teachings don't work, then we should feel free to leave them behind and pursue other paths.
That said, there is also the idea that some attachments are better than others. For example it is probably better for an alcoholic to replace their attachment to alcohol with an attachment to the 12 steps of Alcoholics Anonymous. Likewise, it would be better for someone who is attached to suffering or causing suffering in others to replace that with an attachment to the Buddha's teachings.
Do the teachings of the Buddha cause you suffering? If not, perhaps it's ok to hang on to them for a little while longer on this journey. :)
I find Buddhism refreshing in this manner as the teachings of some other religions actually do cause suffering for their followers. For example people who are excluded from participating fully in their chosen houses of worship due to sexual orientation.
Identifying with something doesn't necessarily mean you're attached to it, especially if that something is just your way of living. I identify best with Zen Buddhism, but I'm not attached to it any more than I'm attached to my own consciousness; it's just become how I think, which dictates how I feel.
Attachments are bad because if you lose them, you suffer. I can't 'lose' Zen without completely losing myself, which is going to happen to all of us one day or another :) Preference is also commonly confused with attachment. I prefer a certain knife in my kitchen drawer for slicing tomatoes, but I wouldn't be at all upset if it wasn't there one day, I'd simply replace it.
A part of daily meditation can be imagining losing that which you value the most, so you've experienced it when it ultimately happens, which softens or even mitigates the suffering that might otherwise ensue. If you can't do that with something, then it's probably not something you could become attached to, but more just a part of your being.
Actually Buddha stated in his suttas after following the Eight Fold Path to attain Nibbana, you should give up the path when you attain the supreme bliss of Nibbana. It is something like this; think that you wanna cross a river. There's no boat near by. So you collect wood and creepers and finally build a small boat and you cross the river using it. After crossing the river, will you carry the boat with you where ever you go thinking "this boat helped me to cross the river"? No. You'll leave the boat by the river and you'll go where you need to go. Buddha state that similarly one should give up the eight fold path after perfectly attaining the supreme bliss of Nibbana.
@THelper to elaborate on Toby's point. To call oneself a buddhist is to identify oneself with an ideological construct and therefore to dwell in a mental fabrication. The ideas of buddhism are arranged into a belief system more commonly known as a view. To associate your self with this view, is exactly the kind of housebuilding which the buddha espoused against in practically every sutra. Buddhism is the only "religion" which fervently encourages its followers to abandon any part of the belief system when it begins to hold them back rather than help them.
I think there is a misunderstanding here. Buddha was not a Buddhist, he was not attached to the previous Buddha (Kassapa) and still the attained the maxium goal. Becoming a Buddha or an Arahant does not require attachment, on the contrary, it requires deattachment and equanimity.
Don't think about Buddhism as a tradicional religion, it is more like an analysis of the laws of the universe (both inside and outside), Buddha was simply explaining how things work, what the mind is, the best path to take and the consequences of good and bad deeds.
You should have confidence and gratitude towards the Buddha. If this becomes a strong attachment this will hinder your progress on the path. The story of Vakkali is a good example.
If you are dealing with Buddhism as a phylosophy then you are dealing with matters at a conceptual level. This is feeding into your perception than helping towards the cessation of perception.
Why is attachment to Buddha not a poison?
Because Buddhism (attachment to Buddha, Sangha, Dharma) has meta-attachment: it teaches to even let go of Buddhism itself--but only once one has mastered Buddhism's practices and not a moment sooner. To be detached from Buddhism a moment sooner would be like a HS student dropping out before he finished.
In short: Buddhism teaches detachment from Buddhism itself. No other tradition does this.