Take an example of the below plot for an LPF (Source : WikiPedia)
The plot starts from $0$. We know that the fourier transform of any signal brings in negative frequencies due to complex exponentials (which are just as real as positive frequencies, just to be clear) but most of the frequency response plots I have observed for practical causal filters, they start from $0$.
I have the following questions: Why do we represent/plot the frequency response of a causal filter with only positive frequency plane? Does it have to do something with making the non-causal ideal sinc filter, a causal one? (But don't we have to make the impulse response [time domain] causal in order to achieve that? [although I don't know what's the frequency response of a causal sinc]) or is it understood that there is a symmetric negative frequency part and we just ignore it?