why shouldn't i universal::isa?

according this

i shouldn't universal::isa() should instead $obj->isa() class->isa().

this means out something anxiety initial place following anxiety category i have do

eval { $poss->isa("class") }

and check $@ gumph, else

use scalar::util 'blessed';
blessed $ref && $ref->isa($class);

my doubt why? what's wrong universal::isa called that? it's many cleaner things like:

my $self = change universal::isa($_[0], __package__)

to presumably duty being called vigilant not. there good purify choice doesn't unwieldy ampersands potentially enlarged lines?