you guys have absolutely no idea what you are talking about...
an ABM missile travelling at mac 3 mac 4 may be 5 is trying to hit a re entry vehicle travelling at mac 15 or mac 20... that means you cannot chase it... its three times faster than the interceptor.
what ABM does is to calculate the ballistic trajectory and contemplates where it would be at said time and send its interceptor for head on collision....
if the target missile changes its ballistic trajectory (df series, shaheen series, topol M) , whole calculations are finished. all these missiles change their trajectory several times before re entry..... final trajectory gives a raction time of not more than 30 seconds....
now go figure
Firstly, speed is more or less an unimportant facet, what matters is the maneuvering capacity of the warhead and the ABM.
Secondly, you are wrong, there is no "chase" being initiated.
Its a head on meet and there is no escaping detection.
This longer trajectory of BMs give ample time for space based detection systems and ground based radars to detect the said BM, specially during its boost phase.
Even more so during an India vs Pakistan scenario, both countries are very close to each other, and any Pak BMs wont need a global SBIRS like system, a few satellites will do and neither will it need a shit load of radars nor the powerful ones like US uses.
Hell most BMs originating in Pak will be detected by ground radars alone, giving our SFC the opportunity to intercept it before it even reaches its apogee, i.e eventually when we make boost phase systems.
I do accept that our BMD is in its nascent stages, rather all BMDs of the world have been ignored.
But we and everyone else is catching up really fast.
Back in the 40s and 50s, due to lack of proper tech and certain "geo political concerns", ABM Treaty and such, ABMs were more or less shelved.
And only now are they being given their due, and if you consider that into account MIRVs and MaRVs have been there for a long time while BMDs have just started to catch up, and they are catching up really bloody fast.
And as technologies advance, countries become richer and the cost-exchange ratio becomes better the more the defensive capabilities of nations will improve.